258 LOWELL— REPULSION OF GASEOUS MOLECULES [April 21, 



80 per cent, of emission bands of carbon monoxide, 

 20 per cent, continuons spectrum, 



the hydrocarbon emission being, at this distance from the head too 

 feeble to show. 



Comparing now the spectrograms taken with a \'oightlander lens 

 and a Cramer Iso. Inst, plate on May 23, 25, 26, 28 and 29 we find 

 that the ratio of the two kinds of light varied in the direction of rela- 

 tively greater emission from the former to the latter date. On May 

 23 itself the plates are affected by moor light so that a direct com- 

 parison of the relative ratios is too difficult to be made a basis of 

 direct comparison, but that of May 28 gives for the ratios in the tail 

 3° from the head : 



70 per cent, emission of carbon monoxide, 



5 per cent, emission of hydrocarbons, 

 25 per cent, continuous spectrum. 



Putting these facts together we shall not be far out of the way 

 in stating the ratio on May 23 of the emissive and continuous spec- 

 trum of the tail at a distance of from 3° to 6° from the head for 

 the 5 plate as 



70 per cent, emission spectrum, CO and CHi, 



30 per cent, continuous spectrum. 



We have then this interesting conclusion : that the knots which 

 showed the action of a repulsive force exerted from the sun were 

 chiefly composed, not of solid particles, but of molecules of gases. 



5. To clinch this deduction I next turned to comet Morehouse. 

 Catechized in this connection it not only corroborated the fact but 

 emphasized it. Before the time of measuring the velocities in the 

 tail of Halley's comet I had done the like for comet Morehouse, the 

 knotted character of its tail offering promising inducement. I was 

 not aware that Mm. Quenisset and Baldet, in France, and Professor 

 J. A. Miller, of Swarthmore, Pa., had measured photographs of this 

 comet in this manner previously and detected the same accelerated 

 motion away from the head which my own later measures showed. 

 My measures have also revealed why certain previous observers such 

 as Barnard at Yerkes and Campbell at the Lick had failed to find 

 such evidence. 



