Royal Society. 303 



We had marked for notice our author's way of treating the 

 subject of proportion; but our limits will not allow us to fulfil our 

 intention. We will only say that it seems to us a feasible way of 

 treating the subject (in the same manner as his treatment of paral- 

 lels is feasible)!; but as to its being an improvement on Euclid's 

 method, that is quite another matter. 



XLIV. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 226.] 



Feb. 26, 1874. — Joseph Dalton Hooker, C.B., President, in the 



Chair. 



'T^HE following communications were read :— 

 -*- " Note on Displacement of the Solar Spectrum." By J. H. 

 N. Hennessey, F.K.A.S. 



The following experiments were made with the (new) spectro- 

 scope (three prisms) of the Eoyal Society, to ascertain for this in- 

 strument the amount of displacement in the solar spectrum from 

 change of temperature. The spectroscope was set up on a pillar 

 within a small tent at a time of the year when the thermal range 

 is considerable : the collimator was placed horizontal, and directed 

 through a window in the tent to a heliostat, which was made to 

 reflect the sun's image when required. On closing the window 

 darkness prevailed in the tent, so that the bright sodium lines 

 were easily obtained from a spirit-lamp. Before commencing, the 

 slit was adjusted and the spectroscope clamped ; and no movement 

 of any kind was permitted in the instrument during the experi- 

 ments. The displacement was measured by means of a micrometer 

 in the eye-end of the telescope, readings being taken (out of curio- 

 sity) successively to both dark and bright lines, i. e. to K 1002*8 =Dr 

 and K 1006-8 =Dv A verified thermometer was suspended directly 

 over and almost touching the prisms. The meteorological obser- 

 vatory referred to was some fifty yards north of the tent. 



Rejecting observation 5 (in the following Table) because the 

 thermometer was evidently in advance of the prisms, we deduce 



By Dark lines, displacement equal 



Dr to Dv is produced by ... . 31'3 change of temperature. 

 By Bright lines, displacement equal 



Dr to Dv is produced by. . . . 29'4 „ 



Mean.... 30 



from which it appears that the displacement in question may not 

 be neglected in investigations made under a considerable thermal 

 range. 



