80 Intelligence and Miscellaneous Articles. 



but I will give a comparative view of the results obtained with a 

 beautiful prism of rock-salt, using as a source of heat either the gas- 

 lamp or Bourbouze's lamp. 



All the arrangements were the same in the two sets of experiments ; 

 in both cases the prism was in the position relative to the minimum 

 deviation of the red, which for the extreme red was 40° 18'. Under 

 these circumstances, working with the Bourbouze lamp, and taking 

 as the unit of effect that obtained in the extreme red, that obtained 

 at half a degree from this position is 2'2, at 1 degree 0*3 only, and at 

 1° 25' it is zero. At the same time the rays of the first three layers 

 are transmitted through a fluor-spar trough containing a layer of 

 water 2 millims. in thickness, in the proportionsof 0'9O,O-6O,andO'75. 



On the other hand, with a bat's-wing burner, taking as unit the 

 effect produced in the extreme red, that obtained at half a degree 

 from this position becomes 4 instead of 2 '2, at 1 degree it is 5 in- 

 stead of 03, and at 2 degrees it is still very appreciable. The spec- 

 trum thus extends much further into the obscure region. But it is 

 far less transmissible through water. For the band at half a degree 

 from the obscure red the transmission is scarcely 0*14 instead of 

 060, and for that at a distance of 1 degree from the red it becomes 

 insignificant. 



Other differences are met with between the spectra furnished by 

 these two sources. With the gas-burner, under the conditions of my 

 experiments, no heat is found either in the yellow or the green, and 

 still less in the extreme white of the spectrum. With Bourbouze's 

 lamp I easily found some in the green, although the intensity of the 

 maximum was not different in the two cases. 



I may also be permitted to adduce the following results. 



Working with Bourbouze's lamp, the transmissibility of rays of 

 the maximum through water seemed a little less than that of the rays 

 which precede or succeed them in the order of refrangibility. 



A similar effect is observed in the solar rays ; I have also observed 

 a similar maximum in investigating the action of a trough full of 

 chloroform on the rays from a gas-burner. 



Iodized chloride of carbon allows all the obscure part of the radia- 

 tion from this source to pass in abundance ; in other words, the 

 transmission through it of the extreme red rays is very little different 

 from that of the other obscure rays ; if there be any difference, it is in 

 favour of the transmissibility of the least-refrangible rays. The lu- 

 minous part of the spectrum is reduced by the action of this absorbent 

 .to two beautiful bands, one red and the other violet, separated by a 

 well-defined dark space. 



The transmissibility through cether diminishes with the refrangibi- 

 lity when a moderator-lamp is used as source of heat ; but it is very 

 appreciable for rays of the maximum. 



All these experiments agree with those I had the honour of pre- 

 senting to the Academy the 9th of last August, to prove that if, in 

 pure spectra, we isolate the pencils formed of rays whose deviations 

 by the same prism are almost identical, these pencils may be very 

 unequally transmissible through the same absorbent if they arise 

 from different sources. — Comptes Rendus, Nov. 30, 1808. 



U 



