344 Prof. Ch. V. Zenger on a New Steam-gauge, 



of it, next the mirror, are in aquilibrio as to temperature, there 

 will be no radiation from either side of the canister ; but, accord- 

 ing as the latter is in a position of greater or less temperature 

 than that of the medium, it will produce increased or diminished 

 temperature of the focal ball, and in each case the varnished 

 side will be most efficient. 



This apparent " radiation of cold " I would call a " negative 

 heat-wave." An analogy with waves in water may make my 

 meaning clear. Thus, if at one end of a narrow channel of still 

 water you immerse a conical-shaped vessel, a regular wave will 

 be propagated to the other extremity of the channel, its surface 

 at the origin of the wave being raised above the equilibrium 

 level. This I call a positive wave. Again, after water-equili- 

 brium has been reestablished, on withdrawing this cone from 

 the water, another wave will be propagated to the further ex- 

 tremity of the channel ; but now the surface at the origin of 

 the wave will evidently be depressed below the equilibrium- level. 

 This, therefore, I would call a negative wave, being a wave of 

 exhaustion, like the wave of cold. 



In conclusion, I have only to add that I believe all the phe- 

 nomena of "absorption" (whether of light or heat) are to be ex- 

 plained on Young's beautiful theory of "interference of waves;" 

 and, notwithstanding the experiments of Forbes, Melloni, and 

 others in reference to the supposed polarization of heat, I con- 

 fess to having grave doubts, being inclined to believe that the 

 distinction between waves of light and of heat will be found to 

 be due to the " setherial vibrations " of the former being always 

 in a plane perpendicular to the progress of the wave, whilst 

 those of the latter take place in the direction of wave-propaga- 

 tion; thus these effects would be due to different functions of 

 the setherial vibrations. Hence the proportionality of light to 

 heat is not to be expected ; and it is easy to understand how a 

 beam (containing both light- and heat-rays) may be sifted of 

 either by transmission through certain substances without any 

 sensible diminution of the other system of rays — a result appa- 

 rently incomprehensible if there is no essential distinction between 

 light and heat. 



XLIV. On a New Steam-gauge. 

 By Professor Ch. V. Zenger*. 



THIS gauge is intended to avoid the defects of common air- 

 gauges, which have hitherto prevented the employment 

 of the air- manometer, and at the same time to be more accurate 



* Communicated by the Author. 



