48 REPORT — 1861. 



shown, the direct action of the moon would affect, and General Sabine has deter- 

 mined its values at several stations scattered over the earth, in calculating- the for- 

 mula3 which best represent the observations. These values range (see the Introduc- 

 tion to the second volume of the ' St. Helena Observations ') from 0"'48 up to 2"'04. 

 There is therefore no gi-oimd for presuming, from the minuteness of the coefficient, 

 that the moon is not of as magnetic, or even much more magnetic materials than 

 the earth. 



If the comparison with the earth be made mass for mass instead of bulk for bulk, 

 the above disturbances must be reduced in the ratio of the moon's density to that of 

 the earth, that is, to about two-thirds of the values already given. 



The same method of course applies equally to the sim ; and whether his magnetic 

 moment be conceived to be gi-eater than that of the earth in proportion to his mass, 

 or in proportion to his bulk, his maximum influence will be even less than that 

 assigned above to the moon ; for he never attains an apparent size as great aa the 

 maximum of the moon, and his density is only about half that of the moon. 



On Liglitning Figures, chiefly with reference to those Tree-like or Mamijted 

 Figures sometimes found on the Bodies of Men and Animals that have been 

 struck by Lightning. By Charles Tomlinson, King's College, London. 



Professor Poey has collected a number of such cases into a memoir, entitled 

 * The Photographic Effects of Lightning,' a second edition of which has been pub- 

 lished at Paris during the present year. One of these cases is the following : — A 

 boy climbed a tree to steal a bird's-nest ; the tree was struck by lightning, and the 

 boy thrown to the ground ; on his breast the image of the tree, with the bird and 

 nest on one of its branches, appeared very plainly. Mr. Tomlinson explains such 

 cases by referring to breath-figures, and showed that when the discharge of a 

 Leyden jar is received on a pane of glass, it bums away a portion of the organic 

 film which covers all matter exposed to the air, so that when breathed upon, the 

 moisture condenses in unbroken streams along the lines where the electricity has 

 passed ; while on the other parts of the surface the moisture condenses in minute 

 globides, so that on holding the glass up to the light the figure is distinctly seen, 

 80 long as the breath remains on the plate. This figm-e resembles a tree, bare of 

 leaves, and might (as the President of the Section afterwards remarked with 

 reference to the diagrams exhibited) be taken for any tree in the world. In this 

 figure we have a broad and somewhat rippled line of least resistance or path of the 

 principal dischai-ge, branching off from which ai'e numerous ramifications, fi-om 

 each of which proceed large twigs, and from these smaller ones of great delicacy 

 and beauty. It can be proved that when the discharge of a Leyden jar is thus 

 received on glass, the jar sends out feelers in all dhections to prepare the way for 

 the line of least resistance, and this being accurately marked out, the principal 

 discharge takes place. In some cases the discharge bifurcates and even trifurcates. 

 If the glass presents too much resistance, the breath-figure consists of thpse feelers 

 only ; and these are the lines which produce the sensation of cobwebs being drawn 

 over the face, which seamen sometimes describe as the forerunners of the ship 

 being struck. The main trunk is hollow, and resembles in its structm'e the siliceous 

 tubes known as Fulgurites. Mr. Tomlinson took this figure to be typical of the 

 lightning discharge which strikes terrestrial objects, and objected to the stereotyped 

 zigzag by which a stroke of lightning is generally represented. His theory is, that 

 when a tree-like impression is found on the body of a man or animal struck by 

 lightning, a portion of the fiery hand of the lightning itself has passed over the 

 Victim and left its mark. Several cases of this kind were described and discussed ; 

 but allowance must be made for the imagination of bystanders, which leads them 

 to see in these ramified impressions "an exact portrait of the tree; " the blotches 

 are taken for leaves, for a bird or bird's-nest, &c., as the case may be. Cases were 

 also examined in which these tree-like impressions were referred by medical men 

 to ecchymosis ; other cases, in which the impressions of a horseshoe, of a nail, of 

 a metal comb, of coins, &c., were found on the persons of the victims, were 

 explained on the principle of the transfer of metallic particles from one conductor 



