KNOBLAUCH ON RADIANT HEAT. 191 



1 shall pass over the manifold difficulties which impeded my 

 observations, and -which entailed a long series of fruitless expe- 

 riments, by which I ultimately succeeded in ascertaining the 

 entire range of disturbing influences, and, as I think, in over- 

 coming them; for every one who engages in these investiga- 

 tions has to learn the elFect of local influences from his own ex- 

 perience ; and an opportunity will hereafter be taken of detailing 

 the minor conditions which must be taken into consideration in 

 the critical examination of the results. 



I. On the Passage of Radiant Heat through Diathermanous 

 Bodies, with especial regard to the Temperature of the Source 

 of -Heat. 

 The results to which such investigations as have hitherto been 



made on the immediate passage of radiant heat through certain 



bodies have led, may be briefly summed up in the following 



positions : — 



1. Heat passes through certain (diathermanous) substances, 

 and this in an immeasurably small space of time. 



2. In one and the same body the quantity of heat transmitted 

 is proportionate to the smoothness of its surface. 



3. The loss which heat suffers on radiating through a sub- 

 stance is less in proportion as it has already penetrated through 

 thicker layers of this substance. 



4. Radiant heat passes through different bodies in different 

 proportions; however the property of bodies to transmit it 

 has no relation to their transparency. 



5. Rays from one and the same source of heat, which are 

 transmitted in succession through different diathermanous sub- 

 stances, experience from this, losses which vary according to the 

 nature of the bodies, and are always greater than those which 

 they experience when transmitted through homogeneous bodies. 



6. Rays of heat, from different sources, which directly pro- 

 duce similar elevations of temperature, pass through one and 

 the same substance in dissimilar proportions. 



resistance to the conduction of the electromotive elements was comparatively 

 small to that of the wire closing the circle, was a simple consequence of Ohm's 

 law. (The Galvanic Circuit, considered Mathematically, by Dr. G. S. Ohm. 

 — Scientific Memoirs, Parts VII. and VIII.) 



In this case, experiment produced a deflection of 26° for a certain intensity 

 of thermo-electrical excitation, when the current ran simply through the length 

 of the wire of the multiplier; but of ."i?" when it sinniltaneously passed through 

 both portions of the coils ; and in another experiment, in the first case, 30° ; and 

 in the second, 60^. 



