Miscellanies. . • 185 



CHEMISTRY. 



1. JVew Experiments in Caloric, by MM. Nobili and Mel- 

 LONi, performed by means of the Thermo-multiplier. (Translated 

 and abridged from the Annales de Chim. et de Phys. Oct. 1831, 

 by C. U. Shepard.) — The Thermo-multiplier is a species of ther- 

 nioscope, which is so delicate an indicator of temperature, as to be 

 sensibly affected by the natural heat of a person, placed at the dis- 

 tance of twenty-five or thirty feet. The principal parts of the in- 

 strument are ; 1st;, a thermo-electric pile ; 2ndly, a galvanometer 

 with two needles, which are specially designed for the thermo-electric 

 currents. It is the first part of this apparatus which constitutes it a 

 thermoscopic instrument ; the second serves simply as an index. 

 The beat excites the electric currents in the pile j these currents 

 pass through two metallic wires which connect the two kinds of ap- 

 paratus together, are transmitted to the galvanometer, and act through 

 their influence upon the steel needle, by causing it to turn round 

 from its natural position of equilibrium with a force more or less stri- 

 king, according to the intensity of the calorific emanation. 



Heat radiates freely through the atmosphere ; it traverses also un- 

 der the radiant form, glass and rock crystal. This would induce us 

 to imagine, that the instantaneous" passage of the rays of heat through 

 bodies, depends upon the same circumstances which allow of their 

 permeability by the rays of light ; or, in other words, that the instan- 

 taneous passage of radiant heat through bodies, depends upon the 

 degree of their transparency. This in fact, is what generally hap- 

 pens ; for the heating rays traverse with more or less facility, selenite, 

 mica, oil, alcohol, and nitric acid. Of this we assured ourselves by 

 the following experiment. Laminae, or strata of these different sub- 

 stances, were placed successively at the extremity of the cylindrical 

 appendix, whose axis was vertical and superior to the reflector. At 

 a certain distance above it, a .ball of iron, heated either in live coals 

 or boiling water, was rapidly passed ; and at the same instant, the steel 

 needle was seen to deviate more or less from its position in equilibrio. 



But if the general law of the rapid movement of the caloric through 

 the transparent substances above mentioned, is thus established, it is 

 altogether the reverse as respects ihe most useful and the most wide- 

 , ly diffused liquid in nature. Water intercepts the instantaneous 

 passage of the calorific rays : it intercepts them entirely; and the 

 obstacle which it opposes to them is so insurmountable, that it is in 



Vol. XXIIl.— No. 1. 24 



