IQO PHILOSOPHICAL TRANSACTIONS. [aNNO 175S. 



the velocity of the water just above bridge, from many experiments, is not 

 greater .than 2^ feet per second. 



Here h — 994 ; c = 820 ; i; = 2^ ; 4a = 64,3596. 



Now^ = 'i«^^= 1,443. 

 2\c 17220 ' 



And 1,443^ = 2,082 ; and 2,082 — 1 = 1,082 = (|^)^ — 1. 



Also .. = (|)^ = 21 ; and £ = ^^^.'^ = 0,0786. 



Then 1,082 X 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. Of the Earthquake in the West Parts of Cornwall, July 15, I757. 

 By the Rev. William Borlase, M. A., F. R. S. p. 499. 



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 8 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, Mr. B. 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, he 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 basins of an equal diameter. From one of these hollows there 

 issued a strong rush of water, about the thickness of a man's wrist, never ob- 

 served there before nor since. About a quarter after 6, p.m. the sky dusky, the 

 wind being at w.n.w., it fell quite calm. At half past 6, being then at Pen- 

 zance, with some company, they were suddenly alarmed with a rumbling noise, 

 as if a coach or waggon had passed near them 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 100 yards distant from them) felt the stone pavement 

 of the room he was in move very sensibly. 



The shock was not equally loud or violent. Its extent was from the isles of 



