20 M. MELLONI ON THE FREE TRANSMISSION 



the rays that are stopped. By performing these operations, and repre- 

 senting the wliole radiation by 1000, we obtain 



Table A. 



Let us imagine the thickest of the screens split into four equal layers ; 

 the quantities of heat falling upon each will be 

 1000, 619, 576, 558, 

 and the quantities lost in successively traversing the four intervals 



381, 424—381, 442—424, 451—442; 

 that is to say, 



381, 43, 18, 9. 

 We shall then have for the ratios of the respective losses to the incident 

 quantities, 



381 43 18 9 



lOOO' 619' 576' 558' 

 or 



0-381, 0*071, 0-031, 0-016. 



Thus the losses continue to decrease with great rapidity as the thickness 

 increases by a constant quantity. 



We have seen that the action of the radiation on the thermomulti- 

 plier commences at the instant when the communications are established, 

 produces the greatest part of its effect in the first five or six seconds, 

 and ceases entirely after a minute and a half. These facts, which are 

 equally true of the direct rays and of those which reach the pile after 

 having passed through screens of any thickness whatsoever, constitute 

 the best proof that caloric is transmitted by radiation through the inte- 

 rior of the diaphanous bodies. If, nevertheless, a new confirmation of 

 this truth were desired, it would be found in the successive diminution 

 of the losses which the rays undergo in crossing the different layers of 

 a transparent medium. Were the heat, whicli is the subject of our im- 

 mediate inquiries, the effect of a species of conducting power, the losses 

 would continually increase from layer to layer, or would remain con- 

 stant, from the moment when the rays penetrated the medium, and 

 could never follow the opposite law of decrease. 



The progressive diminution of the losses is, moreover, entirelj' pecu- 

 liar to the calorific radiation, whose properties in this and in many other 

 respects are altogether different from those of the luminous rays. In 



