PRESIDENT'S ADDRESS. Ixix. 



Berlin and Hamburg observatories have already taken this 

 step, and Paris is meditating a move. Greenwich, so far, 

 has put up with these troubles, and it is to be hoped that 

 such a serious uprooting may be avoided. To show the 

 difference between the present time and 20 30 years ago 

 it may be mentioned that a hundredth of a second of arc can 

 now be determined more accurately than a tenth of a second 

 at the earlier period. These remarks are also borne out by 

 the length of exposure, 38 hours 7 minutes, required in con- 

 nection with researches on the spectra of spiral nebulae 

 carried on lately at the Mount Wilson Observatory. These 

 nebulae are found for the most part to exhibit the spectra of 

 solar-type stars, but a small number give evidence of gaseous 

 radiation. It is believed from certain observations that 

 some nebulae are variable in their brightness ; but the matter 

 is one of much delicacy, and the fact is not yet fully estab- 

 lished. The last theory as to the cause of variability in some 

 stars is that they are Ellipsoids, uniformly luminous and 

 rotating. When the broad side is presented to us the light 

 would necessarily be much greater than when the narrower 

 end was pointing in our direction. This theory apparently 

 accounts satisfactorily for the light changes observed ; and if 

 an Ellipsoid of such a shape is sufficiently stable under such 

 circumstances, it seems a more simple explanation than that 

 of a light and dark body rotating round each other. In some 

 variables, however, such as Algol, where the light becomes 

 suddenly more feeble for a short time at regular intervals, 

 we must fall back on a dark companion or large planet for 

 explanation. It has been discovered by the comparison of 

 photographs taken at different times that the bright and 

 beautifully-coloured star Capella has a faint companion 

 moving in connection with it at the great distance of 

 12' 3.3". Several meteors have been recorded in the past 

 12 months. Two large ones on June 14, one said to be larger 

 than the moon, in the S. of Ireland, which travelled at least 

 490 miles, the other on the Eastern English Coast. One was 

 observed from Bristol on Oct. 7. Another from Oxford with 



