VOL. LXII.] PHILOSOPHICAL TRANSACTIONS. 325 



curred to some electrician before this time. NoUet's and Mr. Wait's invention 

 of threads, projecting shadows on a graduated board, resembled this apparatus 

 of Mr. Henly's, but was a poor and awkward contrivance in comparison with it; 

 nor was Richman's gnomon, though a nearer approach to this construction, at 

 all comparable to it; and the ingenious author of it had no knowledge of either 

 of those methods when he hit on this. 



Many of the effects of my battery, in breaking of glass, and tearing the 

 surface of bodies, Mr. Henly performs by a single jar, only increasing the 

 weight with which the bodies are pressed, while the explosion is made to pass 

 close under them. By this means he raises exceedingly great weights, fre- 

 quently 6 pounds IVoy, and shatters strong pieces of glass into thousands of the 

 smallest fragments; he even reduces thick plate glass by this means to an impal- 

 pable powder. But what is most remarkable is, that when the pieces of glass 

 are thick, and strong enough to resist the shock, they are marked by the explo- 

 sion with the most lively and beautiful colours, generally covering the space of 

 about an inch in length, and half an inch in breadth. 



In some of the pieces which he was so obliging as to send me, these colours 

 lie all intermixed and confused; but in others I observe them to be disposed in 

 prismatic order, in lines parallel to the course of the explosion, and in some I 

 have counted 3 or 4 distinct returns of the same colour. He has lately informed 

 me, that, since he sent me this piece, he has struck these prismatic colours into 

 another mass of glass, in a still more vivid and beautiful manner, the colours 

 shooting into one another. This effect, he says, was produced by making a 2d 

 explosion, without moving any of the apparatus after the first. When the glass 

 in which these colours are fixed is examined, it is evident that the surface is shat- 

 tered into thin plates, and that these give the colours, the thickness of them 

 varying regularly, as they recede from the path of the explosion. 



Besides these improvements, Mr. Henly has likewise, in a very ingenious 

 manner, diversified several of the more entertaining experiments in electricity, 

 particularly in his imitation of the effects of earthquakes by the lateral force of 

 explosions; and he has also hit on several curious facts, that, unknown to him, 

 had been observed before by others : the following particular, however, I believe 

 is new, exciting a stick of sealing wax, and using a piece of tin foil for the 

 rubber ; he found that it would electrify positively, as well as glass rubbed with 

 silk and amalgama. 



XXVII. Meteorological Observations at Ludgvan in Mount's Bay, Cornwall, 

 1771. By fVm. Burlase, D.D., F.R.S. Communicated by Dr. J. Milks, 

 Dean of Exeter, and F. R. S. p. 365. 

 This is a register, similar to former ones, of the barometer, thermometer. 



