The Astrophysical Observatory 431 



could be seen ; but beyond diis litde was known, except the 

 fact that this heat was of different kinds, and possessed of dif- 

 ferent properties, in the same way that hght is possessed of 

 different colors; there was no considerable investigation of 

 the matter, from the lack of any thermometer delicate enough 

 to appreciate the heat in very small portions, and capable of 

 being placed with such precision as to discriminate the posi- 

 tions of these portions one from another. 



Since the beginning of this century, it had been known 

 that there had been made visible to the eye in the Newton- 

 ian spectrum certain sharply defined black lines called, from 

 their discoverer, "F'raunhofer lines," and which we now know 

 are caused by selective absorption in the atmospheres of the 

 sun and of the earth jointly. Some of these are due to our 

 atmosphere alone, and come and go with different states of 

 the weather, affording a direct means of predicting the ap- 

 proach of rain. All of them are of interest in other ways than 

 to the meteorologist, though all are interesting to him also. 



Now, if we take a base line, 

 and at certain intervals, set off 

 upon it perpendicularly lines 

 proportional to the height of ^- 

 the thermometer in the corre- ^ fed ^^^^^^^^^ 

 spending parts of the spectrum, lamanskys curve. 



we obtain some such curve as is shown in the fio-ure. 

 where the portion on the right indicates what is invisible, 

 and shows three interruptions, discovered by Lamansky in 

 1871,^ and which as indicating nearly all that was known 

 before the writer commenced his work may be compared 

 with the curve given later. The invisible portion of the 

 spectrum contains a great deal more energy than all the 



1 Lamansky M. S. "On the Heat-Spectrum of the Sun .and the Lime-light." London, 

 Edinburgh, and Dublin Philosophical Magazine, Volume LXlii, 1872, page 282. 



