NATURAL PHILOSOPHY. 129 



pence. The reflection of the light might be seen for two miles 

 I'ound. So bright was it that the fire-engine authorities mistooli it 

 for an ordinary conflagration, and hurried their engines to the 

 spot. On finding no trace of the fire they returned, rather cha- 

 grined ; not, however, without first satisfying themselves by a thor- 

 ough examination of the premises. All around appeared one blaze 

 of liglit; the sky looked like a mass of fire." The 25icture taken 

 during this startling illumination " came out," we are told, "with 

 great sharpness and vividness, the houses near being brought out 

 prominently. It, in fact, equalled any picture taken on a bright 

 day." — IlecJianics'' Magazine. 



THE MICRO-SPECTKOSCOPE. 



The micro-spectroscope has received its first application to 

 medico-legal purposes, in the examination for blood stains of the 

 hatchet supposed to have been used in the Aberdare murder. 

 Dr. Bird Herapath, F.R.S., who was retained by the Crown, 

 placed sections of the handle in distilled water, and submitted the 

 solution obtained to an examination in this instrument. Within 

 the green, and on the border of the yellow raj's, the well-known 

 characteristic dark bands of blood were produced. Only one 

 other substance was known to produce similar dark bands, — 

 cochineal dissolved in ammonia, — in ■which case, however, their 

 position would be diflerent. Dr. Herapath said he was satisfied, 

 from the evidence this test had aflorded, that the hatchet had 

 been stained with blood. 



INVISIBLE PHOTOGRAPHIC IMAGE. 



M. Carey Lea of Philadelphia communicates to the " American 

 Joui'nal of Science," for July, 1S65, the following paj^er : — 



" Some experiments in which I have lately been engaged seem 

 to me to finally settle the long-contested question as to the nature 

 of the invisible photographic image, and I hasten to send a very 

 brief description of them. 



" The view that the change which takes place in an iodo- 

 bromized plate in the camera is a purely physical one, that no 

 chemical decomposition takes place, and neither liberation of 

 iodine nor reduction of silver, has obtained a pretty general 

 acceptance. But latterly it has been opposed by two distin- 

 guished photographers. Dr. Vogel and Major Russell. The for- 

 mer aflirms that iodid of silver is never sensitive unless there is a 

 body present capable of taking iodine from it under the influence 

 of light; and Russell l^elieves that the developed image is chiefly 

 produced at the expense of the silver haloid in the film. The 

 following experiments seem to me to decisively close this con- 

 troversy in favor of the physical theory. 



'■'Experiment 1. — If the iodid or bromid of silver in the film 

 undergoes decomposition in. the camera, and, still more, if the 

 developed image is formed at its expense, the film of iodo-bromid 

 must necessarily be greatly consumed in the development under 



