1835.] Scientific Intelligence. 237 



fair to enable us soon to develope completely the cause of the pheno- 

 mena dependent on the presence of this important principle, is the 

 adaptation of the thermo-multiplier as a delicate indicator of sensible 

 heat. All the experiments which had been previously made on this 

 subject were performed by means of Leslie's differential thermometer, 

 which although comparatively, as to other instruments a delicate 

 contrivance, is surpassed in an infinite degree by the thermo-multi- 

 plier. The multiplier consists of about 30 pairs of bars of bismuth 

 and antimony ; the elements being so extremely delicately formed 

 that the extremities present a surface of ~ of an inch square. These 

 are made to communicate with the multiplier, by means of wires 

 leading from the extreme bars. The multiplier consists of a coil of 

 silver wire, armed with silk, and having a magnetic needle so placed 

 in a free space within the centre of the coil, as to enable it to oscillate 

 readily. Now, it was observed by Melloni, that when heat, even 

 that of the hand, is applied to the pile, a powerful effect is produced 

 upon the needle of the multiplier, which undergoes an immediate 

 declination, and traverses an arc more or less great if the heat is 

 constant in a constant interval. It is quite obvious, therefore, that 

 this must be a most excellent thermoscope, and must be admirably 

 adapted to the delicacy which is necessary in experimenting in re- 

 ference to heat. Provided, then, with this apparatus, Melloni set 

 about examining accurately the relations of heat and light, a problem 

 which philosophers have long been endeavouring to elucidate. For 

 this purpose, he studied permeability of heat through different bodies. 

 Mariotte concluded, from his experiments, that the heat of a common 

 fire does not pass through glass, or at least, in very minute quantity. 

 Scheele went further, and decided that not a ray of heat traversed 

 glass. Pictet, however, repeated Scheele's experiment, and obtained 

 a contrary result. From these observations, and those of Herschel, 

 it was inferred that heat does not pass through diaphanous substances, 

 with the exception of atmospheric air. Prevost and Delaroche, by 

 ingenious adaptations, proved, however, that heat is transmitted 

 directly through glass, independent of its conducting power, and this 

 fact has been allowed, with few exceptions, by all philosophers. 

 But although this admission was made, the subject was involved in 

 great obscurity, and presented an inviting field of inquiry to the 

 ingenuity of Melloni. No examination had been instituted into the 

 influence of the state of the surface, of the thickness of the substances 

 through which the heat was transmitted, or of their internal struc- 

 ture upon permeating heat. These, however, were taken up by 

 Melloni, and he is still engaged in the prosecution of his researches. 

 It is easy to see how the different relative diathermal powers or 

 capacities of bodies for transmitting heat could be determined by the 

 apparatus of Melloni, for all that was required was to interpose the 

 substance whose powers were to be investigated, between a steady 

 heat and the voltaic pile, when their capacities would be indicated by 

 the rapidity of the action upon the needle. That the heat is actually 

 transmitted, and does not pass by conduction, is proved by the fact 

 that the internal portions of the glass do not instantly become heated, 

 which is demonstrated by placing a glass screen in front of the pile, 

 nd intercepting the communication with the source of heat. The 



