NATURAL PHILOSOPHY. 137 







that it is indispensable, before formulating general principles, to multiply 

 experiments in a place serving as a permanent observatory, then in flat 

 countries and amongst mountains, on the margins of rivers and water courses, 

 and on the sea shore, in countries like Holland, where there are large alluvial 

 tracts, in salt marshes, &c. Then, and then only, shah 1 we be able to judge 

 of the importance of the subject with which I am occupied, and which is 

 connected with one of the greatest questions in terrestrial physics. 



ON THE FOR3I OF LIGHTNING. 



Mr. Nasmyth, at the British Association, 1856, said that the form usually 

 attributed to lightning by painters and in works of art was very different from 

 that which he had observed as exhibited in nature, and from observing this 

 he was induced to call attention to it. He believed the error of the artists 

 originated in the form given to the thunderbolt in the hand of Jupiter as sculp- 

 tured by the early Greeks. The form of lightning as exhibited in nature was 

 simply an irregular curved line, shooting from the earth below to the cloud 

 above, and often continued from the cloud downwards again to another distant 

 part of the earth. This appearance, he conceived, was the result of the rapidly 

 shooting point of light which constituted the true lightning, leaving on the 

 eye the impression of the path it traced. In very intense lightning, he had 

 also observed offshoots of an arborescent form to proceed, at several places, 

 from the primary track of the flash. 



This communication gave rise to an animated discussion, as to whether or 

 not the flash of lightning was the effect of a rapidly moving point of light, 

 and if so, whether the direction was. as stated by Air. Nasmyth, in nine cases 

 out of ten from the earth to the cloud, or the contrary. Mr. Kasmyth adduced 

 the manner in which leaden pipes were burst, they being bad conductors 

 of electricity, as proofs of his views of which he instanced one which 

 had been burst in several places, from the bottom to the top, in Edinburgh, 

 during a thunderstorm, the pieces of which Sir J. Leslie had obtained and 

 placed in his physical class room. On being questioned, however, by some 

 members of the sectiot, as to how these distant burstings outwards along the 

 pipe gave any indication of the direction, it did not appear there were any 

 decisive marks indicating this. 



ON THE APPARENT CONVERSION OF ELECTRICITY INTO 3LECHANI- 



CAL FORCE. 



The following is an abstract of a paper communicated to the Philosophical 

 Magazine (London), by "W. E. Grove, detailing a series of experiments, appa- 

 rently showing the conversion of electricity into mechanical force : 



His object was to show, that when electricity performs any mechanical work 

 which does not return to its source, electrical power is lost. The first experi- 

 ment was made in the following manner : A Leyden jar, of one square foot 

 coated surface, has its interior connected with a Cuthbertson's electrometer, 

 between which and the outer coating of the jar are a pair of discharging balls 

 fixed at a certain distance (about hah an inch apart). Between the Leyden jar 



