Mr. C. V. Walker on Lightning Conductors. 311 



his reasons for excluding Leyden jars from this inquiry, and glanced 

 at the importance of establishing such a position, he proceeds to 

 throw sparks from the machine into wires arranged to represent 

 lightning rods, and makes his observations upon the effects produced 

 by these wires. Some of them pass perpendicularly between the con- 

 ductor and the earth, others are led off horizontally : all give rises to 

 the said " lateral spark." The next point was to show that these wires 

 did resemble lightning-rods ; and for this purpose an arrangement 

 was made, as closely resembling nature as possible : a brass rod, 

 terminating in a ball, was erected beneath a similar ball proceeding 

 from the prime conductor of the machine, and sparks were passed 

 between the two : beside the rod was held a smaller and shorter 

 one, also terminating in a ball ; the larger rod was screwed into a 

 brass disc, the smaller rested on the floor ; each was separately con- 

 nected with a good discharging train. All things being in order, 

 sparks were thrown from the prime conductor, and " lateral sparks" 

 passed in abundance between the rods : and if this represented a 

 lightning rod, it appeared lawful to infer that in every other arrange- 

 ment when sparks were obtained, they proceeded from the wires 

 being a representation of a lightning rod. Without entering into 

 the various experiments, all tending to develope the same truth, we 

 come to show the explanation this last affords of the action of an 

 elevated rod between two metallic discs. 



It is well known that such a rod will not give off sparks to vicinal 

 bodies ; but Mr. Walker is of opinion that this want of the la- 

 teral discharge is due to the fact that the vicinal body rests on the 

 lower disc, and is thus a direct metallic connexion with the main rod ; 

 in proof of which he shows, that the sparks in his experiment just 

 noticed, ceases the instant the end of the lower rod touches the 

 disc; and thus too are confirmed the principles described in his 

 former paper, by which the safety of lightning rods is ensured by 

 establishing such contact. 



3. " On a new form of Battery, particularly adapted to Blasting 

 Rocks," &c. By Martyn Roberts, Esq., F.R.S. Ed., Memb. 



This battery consists of alternate and parallel plates of iron and 

 zinc, and is excited by sulphuric acid 1 + , water 30 : the plates are 

 supported in a frame, by which they can readily be immersed in the 

 trough of liquid (which may be of wood luted with white lead), and 

 be removed at the termination of the experiment. The peculiar 

 features of this battery in contradistinction to others, are the modes 

 of connecting the plates. If we consider the figures 1, 2, 3, 4, &c. 

 to represent the zinc plates, and the letters a, b, c, d, &c. the iron, 

 a and b must be first connected ; then 1 and c, 2 and d, 3 and e, and 

 so on, by which means both sides of each plate are brought into re- 

 quisition, and no counter currents reduce the action. Mr. Roberts 

 recommends a series of twenty for blasting, and says that they may 

 be comprised within a space of eight inches. 



4. Electro-Meteorological Register for June, by W. H. Weekes, 

 Esq., Memb. 



Aug. 16.— A Letter from Walter Hawkins, Esq., F.S.A., F.Z.S., 



