Philosophical transactions, Vol. L. Part II. For the year 1758.

Altho’ the breadth of the river at Westminster-bridge is 1220 feet; yet, at the time of the greatest fall, there is water thro’ only the thirteen large arches, which amount to 820 feet: to which adding the breadth of the twelve intermediate piers, equal to 174 feet, gives 994 for the breadth of the river at that time: and the velocity of the water just above bridge (from many experiments) is not greater than 2¼ feet _per_ second.

Here _b_ = 994; _c_ = 820; _v_ = 2¼; 4_a_ = 64,3596.

Now 25_b_ ⁄ 21_c_ = 24850 ⁄ 17220 = 1,443.

And 1,443² = 2,082; And 2,082 - 1 = 1,082 = (25_b_ ⁄ 21_c_)² - 1.

Also _vv_ = (⁹⁄₄)² = ⁸¹⁄₁₆; And _vv_ ⁄ 48 = 81 ⁄ (16 × 64,3696) = 0,0786.

Then 1,082 × 0,0786 = 0,084 feet, the fall sought.

Which is about 1 inch; and is about half an inch more than the greatest fall observed by Mr. Labelye.

LXIV. _An Account of the Earthquake in the West Parts of_ Cornwall, July _15th 1757. By the Rev._ William Borlase, _M. A. F.R.S. Communicated by the Rev._ Charles Lyttelton, _LL.D. Dean of_ Exeter, _F.R.S._

[Read Jan. 26, 1758.]

ON Friday the 15th of July, 1757. a violent shock of an earthquake was felt in the western parts of Cornwall.

The thermometer had been higher than usual, and the weather hot, or calm, or both, for eight days before; wind east and north-east. On the 14th in the morning, the wind shifting to the south-west, the weather calm and hazy, there was a shower. The afternoon hazy and fair, wind north-west. The barometer moderately high, but the mercury remarkably variable.

On the 15th in the morning, the wind fresh at north-west, the atmosphere hazy. Being on the sands, half a mile east of Penzance, at 10 A. M. near low water, I perceived on the surface of the sands a very unusual inequality: for whereas there are seldom any unevennesses there, but what are made by the rippling of the water, I found the sands, for above 100 yards square, all full of little tubercles (each as large as a moderate mole-hill), and in the middle a black speck on the top, as if something had issued thence. Between these convexities were hollow basons of an equal diameter. From one of these hollows there issued a strong rush of water, about the bigness of a man’s wrist, never observed there before nor since.

About a quarter after six, P. M. the sky dusky, the wind being at west north-west, it fell quite calm. At half past six, being then in the summer-house at Keneggy, the seat of the Hon. J. Harris, Esq; near Penzance, with some company, we were suddenly alarmed with a rumbling noise, as if a coach or waggon had passed near us over an uneven pavement; but the noise was as loud in the beginning and at the end, as in the middle; which neither the sound of thunder, or of carriages, ever is. The sash-casements jarred: one gentleman thought his chair moved under him; and the gardener, then in the dwelling house (about an hundred yards distant from us) felt the stone pavement of the room he was in move very sensibly.

In what place the shock began, and whether progressive or instantaneous in the several places where it was felt, is uncertain, for want of accurately determining the precise point of time in distant places.

The shock was not equally loud or violent. Its extent was from the isles of Scilly eastward as far as Liskerd, and towards the north as far as Camelford; thro’ which district I shall trace it, according to the best informations I could procure.

In the island of St. Mary, Scilly, the shock was violent. On the shores of Cornwall, opposite to Scilly (in the parish of Senan, near the Land’s-end) the noise was heard like that of a spinning-wheel on a chamber-floor. Below stairs there was a cry, that the house was shaking; and the brass pans and pewter rattled one against another in several houses in the same parish. In the adjoining parish of St. Just, two young men being then swimming, felt a strong and very unusual agitation of the sea. In the town of Penzance, in one house the chamber-bell rung; in another the pewter plates, placed edgeways on a shelf, shifted, and slid to one end of the shelf: and it was every-where perceived more or less, according as people’s attention was engaged.

At Trevailer, the seat of William Veale, Esquire, about two miles from Penzance, the noise was heard, and thought at first to be thunder: the windows shook, and the walls of the parlour, where Mr. Veale sat, visibly moved. The jarring of the windows continued near half a minute; but the motion of the walls not quite so long: and some masons, being at work on a contiguous new building, the upright poles of the scaffolds shook so violently, that, for fear of falling, they laid hold on the walls, which, to their still greater surprize, they found agitated in the same manner. And a person present, who was at London at the time of the two shocks in the year 1751, thought this shock to resemble the second, both in degree and duration[10].

At Marazion, the next market-town east of Penzance, the houses of several persons shook to that degree, that people ran out into the street, lest the houses should fall upon them.

In the borough of St. Ives, on the north sea, six miles north of Penzance, the shock was so violent, that a gentleman, who had been at Lisbon during several shocks, said, that this exceeded all he had met with, except that on the 1st of November 1755, so fatal to that city.

At Tehidy, the seat of Francis Basset, Esq; the rooms shook, and the grounds without doors were observed to move. The shock was felt sensibly at Redruth, St. Columb, Bodman, _&c._ along to Camelford, which is about 90 miles from the isle of Scilly. From Marazion eastward it was felt at several places in like manner, as far as Lostwythyel; but at Liskerd, about ten miles east of Lostwythyel, it was but faintly perceived, and that by a few persons. It was still less sensible at Loo and Plymouth, “scarcely sufficient to excite curiosity or fear”[11].

The times of its duration were various. At Keneggy we thought the noise could not have lasted above six seconds; at Trevailer, not two miles distant to the west, it was thought to have lasted near half a minute; in the parish of Gwynier half a minute; at Ludgvan, three miles east of Penzance, the noise was rather longer than half a minute; but the shaking felt in the garden, and observed in the houses, short and momentary. In Germo great Pinwork, seven miles east of Penzance, it lasted only a few seconds; but in the isles of Scilly it was computed at 40 seconds.

Thus was this earthquake felt in towns, houses, and grounds adjacent; but still more particularly alarming in our mines, where there is less refuge, and consequently a greater dread from the tremors of the earth.

In Carnorth adit, in the parish of St. Just, the shock was sensibly felt 18 fathom deep; in the mine called Boscadzhill-downs, more than 30 fathom.

At Huel-rith mine, in the parish of Lannant, people saw the earth move under them, first quick, then in a slower wavy tremor; and the stage-boards of the little winds or shafts 20 fathom deep were perceived to move.

In Herland mine, commonly called the Manor, in the parish of Gwynier, the noise was heard 55 and 60 fathom deep, as if a studdle[12] had broke, and the deads[13] were set a running. It was nothing like the noise of thunder.

In Chace-water mine the same noise was heard, at least 70 fathom under the surface.

At Huel-rith mine, near Godolphin, the noise was seemingly underneath. I felt (says the director of the mine) the earth move under me with a prodigious swift, and apparently horizontal tremor: its continuance was but for a few seconds of time, not like thunder, but rather a dull rumbling even sound, like deads running under ground. In the smith’s shop the window-leaves shook, and the slating of the house cracked. The whim-house shook so terribly, that a man there at work ran out of it, concluding it to be falling. Several persons then in the mine, working 60 fathom deep, thought they found the earth about them to move, and heard an uncommon noise: some heard the noise, and felt no tremor; others, working in a mine adjoining called Huel-breag, were so frightened, that they called to their companions above to be drawn up from the bottoms. Their moor-house was shaken, and the padlock of their candle-chest was heard to strike against the staples. To shew, that this noise proceeded from below, and not from any concussion in the atmosphere above, this very intelligent captain of the mine[14] observes, from his own experience, that thunder was never known to affect the air at 60 fathoms deep, even in a single shaft pierced into the hardest stone; much less could it continue the sound thro’ such workings as there are in this mine, impeded in all parts with deads, great quantities of timber, various noises, such as the rattling of chains, friction of wheels and ropes, and dashing of waters; all which must contribute to break the vibrations of the air as they descend: and I intirely agree with this gentleman’s conclusion, that thunder, or any other noises from above in the atmosphere, could not be heard at half the depth of this mine. This therefore could be no other than a real tremor of the earth, attended with a noise, owing to a current of air and vapour proceeding upwards from the earth.

I do not hear of any person in those parts, who was so fortunate as to be near any pool or lake, and had recollection enough to attend to the motion of the waters; but it may be taken for granted, that during the tremors of the earth the fluids must be more affected than the solids: nay, the waters will apparently be agitated, when there is no motion of the earth perceptible, as was the case of our ponds and lake-waters in most parts of Britain on the 1st of November 1755. Whence this happens is difficult to say: whether the earth’s bosom undergoes at such times a kind of respiration, and alternately emits and withdraws a vapour thro’ its most porous parts sufficient to agitate the waters, yet not sufficient to shake the earth; or whether the earth, during the agitation of the waters, does rock and vacillate, tho’ not so as to be sensible to man; is what I shall leave to future inquiry.

Earthquakes are very rare in Cornwall. This was but of short duration, and did no harm any-where, as far as I can learn; and it is to be hoped not the sooner forgotten for that reason; but rather remembered with all the impressions of gratitude suitable to an incident so alarming and dangerous, and yet so inoffensive.

LXV. _Some Observations upon the Sleep of Plants; and an Account of that Faculty, which_ Linnæus _calls_ Vigiliæ Florum; _with an Enumeration of several Plants, which are subject to that Law. Communicated to_ Wm. Watson, _M. D. F.R.S. by Mr._ Richard Pultney _of_ Leicester.

[Read Jan. 26, 1758.]

ACosta and Prosper Alpinus, who both wrote near the conclusion of the XVIth century, are, I believe, the first, who recorded that nocturnal change in the leaves of plants, which has since been called _somnus_. It is an observation indeed as old as Pliny’s time, that the leaves of trefoil assume an erect situation[15] upon the coming of storms. The same is observable of our wood-sorrel; and Linnæus adds, of almost all plants with declinated stamina[16]. In the _Trifolium pratense album C. B._ or common white-flowered meadow trefoil, it is so obvious, that the common people in Sweden remark, and prognosticate the coming of tempests and rain from it.

The examples of sleeping plants instanced by Alpinus are but few. That author says, it was common to several Egyptian species[17]; but specifies only the Acaciæ, Abrus, Absus, Sesban, and the Tamarindtree. Cornutus some time afterwards remarked this property in the Pseudo-acacia Americana. From that time it has remained almost unnoticed, till Linnæus, ever attentive to nature’s works, discovered that the same affair was transacted in many other plants; and his observations have furnished us with numerous and obvious examples thereof. Mr. Miller mentions it in the _Medicago arborea Lin. Sp. Pl. 778_. and we may add to the list two other common plants not mentioned by Linnæus: these are the _Phaseolus vulgaris_, common kidney-bean; and the _Trifolium pratense purpureum majus_, or clover-grass: in both which this nocturnal change is remarkably displayed. Doubtless the same property exists in numberless other species; and future observation will very probably confirm Dr. Hill’s sentiment, that no “plant or tree is wholly unaffected by it.”

It is now more than twenty years since Linnæus first attended to this quality in plants. In his _Flora Lapponica_, when speaking of the _Trifolium pratense album_, as above-mentioned, he remarks, that the leaves of the Mimosa, Cassia, Bauhinia, Parkinsonia, Guilandina, and others in affinity with them, were subject to this change in the night time: and he had then carried his observations so far, as to find, that heat and cold were not the cause of this quality; since they were alike influenced by it when placed in stoves, where the temperature of the air was always the same.

The merit of reviving this subject is therefore due to the illustrious Swede; and the naturalist is greatly indebted to him for so far extending his observations thereon.

The subject of the _somnus plantarum_ cannot but be highly entertaining to the lovers of natural knowlege: and such, I apprehend, cannot be less entertained with that faculty, which Linnæus calls _vigiliæ florum_; of which we shall give a brief account.

Previous to our explanation of this affair it is proper to observe, that the flowers of most plants, after they are once opened, continue so night and day, until they drop off, or die away. Several others, which shut in the night-time, open in the morning either sooner or later, according to their respective situation in the sun or shade, or as they are influenced by the manifest changes of the atmosphere. There are however another class of flowers, which make the subject of these observations, which observe a more constant and uniform law in this particular. These open and shut duly and constantly at certain and determinate hours, exclusive of any manifest changes in the atmosphere; and this with so little variation in point of time, as to render the phænomenon well worth the observation of all, whose taste leads them this way.

This faculty in the flowers of plants is not altogether a new discovery; but we are indebted to the same hand for additional observations upon this head likewise. It is so manifest in one of our common English plants, the _Tragopogon luteum_, that our country people long since called it _John-go-to-bed-at-noon_. Linnæus’s observations have extended to near fifty species, which are subject to this law. What we find principally upon this subject is in the _Philosophia Botanica_, p. 273. We will enumerate these plants, and mention the time when the flowers open and shut, that those, who have opportunity and inclination, may gratify themselves, and probably at the same time extend this branch of botanic knowlege still farther.

It is proper to observe, that as these observations were made by Linnæus in the academical garden at Upsal, whoever repeats them in this country will very probably find, that the difference of climate will occasion a variation in point of time: at least this will obtain in some species, as our own observations have taught us; in others the time has corresponded very exactly with the account he has given us.

Whether this faculty hath any connexion with the great article of fecundation in the oeconomy of flowers, I cannot determine: in the mean time it is not improbable. Future and repeated observations, and well-adapted experiments, will tend to illustrate this matter, and it may be lead the way to a full explanation of the cause.

1. Anagallis flore phœniceo C. B. pin. 252. Raii Syn. p. 282. Anagallis arvensis Lin. Spec. plant. p. 148. _The Male Pimpernel._ The flowers of this plant open about eight o’clock in the morning, and never close till past noon. This plant is common in kitchen-gardens and in corn-fields, and flowers in June, and continues in flower three months.

2. The Anagallis cærulea foliis binis ternisve ex adverso nascentibus C. B. pin. p. 252. Raii Hist. Plant. p. 1024. Anagallis Monelli Sp. plant. 148. _Blue-flowered Pimpernel with narrow leaves._ The flowers of this plant observe nearly the same time in opening and shutting as the foregoing.

3. Convolvulus peregrinus cæruleus folio oblongo C. B. pin. 295. Convolvulus tricolor Sp. plant. 158. _Little blue Convolvulus, or Bindweed._ This opens its flowers between the hours of five and six in the morning, and shuts them in the afternoon.

4. Phalangium parvo flore ramosum C. B. pin. 29. Raii Hist. Pl. 1193. _Branched Spiderwort with a small flower._ These open about seven in the morning, and close between the hours of three and four in the afternoon.

5. Lilium rubrum Asphodeli radice C. B. pin. 80. Hemerocallis fulvus Sp. pl. 324. _The Day Lily._ The flowers open about five in the morning, and shut at seven or eight in the evening.

6. Plantago aquatica minor. Park. 1245. Raii Syn. 257. Alisma ranunculoides Sp. pl. 343. Fl. Suec. 2. Nº. 325. _The lesser Water-Plantain_, during its flowering-time, only opens its flowers each day about noon.

7. Caryophyllus sylvestris prolifer C. B. pin. 209. Raii Syn. 337. Dianthus prolifer Sp. pl. 410. _Proliferous Pink._ The flowers expand about eight in the morning, and close again about one in the afternoon.

8. Spergula purpurea J. B. III. 722. Raii Syn. p. 351. Arenaria rubra. Sp. pl. 423. _Purple Spurrey._ These expand between nine and ten in the morning, and close between two and three in the afternoon. This little plant is common among the corn in sandy soils, and flowers in June.

9. Portulaca latifolia sativa C. B. pin. 288. Portulaca oleracea Sp. pl. p. 445. _Common Purslain_, opens its flowers about nine or ten in the morning, and closes them again in about an hour’s time.

10. Ficoides Africana, folio plantaginis undulato micis argenteis adsperso Boerh. Ludg. I. p. 291. Mesembryanthemum chrystallinum Sp. pl. 480. _Diamond Ficoides._ The flowers of this plant open at nine or ten, and close at three or four in the afternoon.

11. Ficoides Africana folio tereti in villos radiatos abeunte. Tourn. Mesembryanthemum barbatum Sp. pl. 482. The flowers of this species expand at seven or eight in the morning, and close about two in the afternoon.

12. Ficoides folio tereti Neapolitana flore candido Herm. Ludg. 252. Kali Crassulæ minoris foliis C. B. pin. 289. Mesembryanthemum nodiflorum Sp. pl. 480. The flowers of this plant open at ten or eleven in the morning, and close at three in the afternoon.

13. Mesembryanthemum folio linguiformi latiore Dillen. Hort. Elth. Mesembryanthemum linguiforme Sp. pl. 488. _Ficoides with a tongue-shaped leaf._ These open at seven or eight in the morning, and are closed about three in the afternoon.

14. Nymphæa alba J. B. III. 770. Raii Syn. 368. Nymphæa alba Sp. pl. 510. Fl. Suec. 2. Nº. 470. _White Water Lily._ This plant grows in rivers, ponds, and ditches, and the flowers lie upon the surface of the water. At their time of expansion, which is about seven in the morning, the stalk is erected, and the flower more elevated above the surface. In this situation it continues till about four in the afternoon, when the flower sinks to the surface of the water, and closes again.

15. Papaver erraticum nudicaule flore flavo odorato Dillen. Hort. Elth. 302. Papaver nudicaule Sp. pl. p. 507. _Wild Poppy with a naked stalk and a yellow sweet-smelling flower._ The flower of this plant opens at five in the morning, and closes at seven in the evening.

16. Alyssoides incanum, foliis sinuatis Tourn. Inst. 213. Alyssum sinuatum Sp. pl. 651. _Hoary Madwort with sinuated leaves._ The flowers of this plant expand between the hours of six and eight in the morning, and close at four in the afternoon.