232 PROCEEDINGS OP THE AMERICAN ACADEMY 



ment, tlms originally made by me, presented a communication to the 

 French Academy of Sciences. They had observed the antagonizing 

 action above referred to, and had seen the infra-spectral lines a, ^, y. 

 They had taken the precaution to deposit with the Academy a sealed 

 envelope, containing an account of their discovery, not knowing that 

 it had been made and published long previously in America. 



Sir J. Herschel had made some investigations on the distributioc of 

 heat in the spectrum, using paper blackened on one side and moistened 

 with alcohol on the other. He obtained a series of spots or patches, 

 commencing above the yellow and extending beyond the red. Some 

 writers on this subject have considered that these observations imply 

 a discovery of the lines a, /3, y. They forget, however, that Hers >liel 

 did not use a slit, but the image of the Sun, — an image which was 

 more than a quarter of an inch in diameter. Under such circumstances, 

 it was impossible that these or any other of the fixed lines could be 

 seen. 



I have many times repeated this experiment, but could not obtain 

 the same result, and therefore attributed my want of success to unskil- 

 fulness. More recently Lord Eayleigh (Phil. Mag., November, 1877), 

 having experimented in the same direction, seems to be disposed to 

 atti'ibute these images to a misleading action of the prism employed. 

 Whatever tlieir cause may be, it is clear that they have nothing to do 

 with the fixed lines a, /3, y, now under consideration. 



In these experiments, and also in others made about the same time 

 on the distribution of heat in the spectrum, I attempted to form a dif- 

 fraction spectrum without the use of any dioptric media, endeavoring 

 to get rid of all the disturbances which arise through the absorptive 

 action of glass by using as the grating a polished surface of steel on 

 which lines had been ruled with a diamond, and employing a concave 

 mirror instead of an achromatic lens ; and, though my resTilts were im- 

 perfect and incomi^lete, I saw enough to convince me that it is abso- 

 lutely necessary to employ a spectrum that has been formed by 

 reflection alone. (Phil. Mag., March, 1857, p. 155.) 



In 1871, M. Lamanski succeeded in detecting these lines or bands 

 by the aid of a thermoniultiplier. He was not adequately informed 

 on what had already been done in the matter in America, for he says 

 that " with the exception of Foucault and Fizeau, in their well-known 

 experiments on the interference of heat, no one as yet has made refer- 

 ence to these lines." Nearly thirty years before the date of his memoir 

 I had pul)Ushed an engraving of tliem. (Phil. Mag., May, 1843.) 



After I had discovered these three lines, I intended to use the grat- 



