778 Htfr. 3. Satterly on the Absorption of 



the same width. Just how the carborundum crystal managed 

 to rule such a groove I am unable to say. A coloured 

 drawing of this very remarkable set of spectra will be Jound 

 in ' Physical Optics.' 



These cases will be more fully discussed in a subsequent 

 paper, in which a full report of an investigation made in 

 collaboration with Prof. A. Trowbridge, of Princeton, with 

 his remarkably perfect yacuum spectrometer will be given. 

 This investigation has shown that these gratings give far 

 higher resolving powers in the- infra-red than have ever been 

 available previously, coml ined with great efficiency. The 

 emission band of C0 2 from the flame of a Bunsen burner, 

 which has been observed only as a single band up to this 

 time, was easi y resolved into three or possibly four com- 

 ponent bands. 



Furl her experimenting will probably improve the quality 

 of the gratings and open up a large field of work in the 

 infra-red re-ion. The gratings yield excellent replicas which 

 can be mounted on flat plates of glass and gold-plated by 

 the cathode discharge. The replicas will very possibly have 

 flatter surfaces than the original gratings, if properly 

 mounted. 



LXXXVI. Some, experiments on the Absorption of Radium 

 Kmanation by Coconut CJutrcoaL By John Sattekly, 

 A.R.C.Sc, B.Sc, B. A., St. John's College, Cambridge*. 



DUKlNfx the performance of some experiments f by the 

 author on the measurement of the amount of radium 

 emanation in atmospheric air by the charcoal absorption 

 method, the following interesting points came up for con- 

 sideration : — 



(a) Is the amount of emanation absorbed from the air 

 always the same fraction of the total amount in the 

 air whatever that amount may be, other experimental 

 conditions remaining the same ? 



(A) In the case when the air flowing to the charcoal 

 contains a constant percentage of emanation, is the 

 amount absorbed by the charcoal proportional to the 

 time the air-current is flowing, or does the charcoal 

 show signs of saturation ? 



(»•) Does the amount of emanation absorbed from the air 

 depend on the humidity of the air ? 



(d) What is the percentage of emanation absorbed in any 

 particular case ? 



* Communicated nv Sir J. J. Thomson, F.II.S. 

 t See Pliii. Majr. Get. 1908 and duly 1^10,' 



