BY G. E. SMALLEY, ESQ. 339 



and refined observations made with instruments of the highest 

 class by the practised astronomical observer. 



Though previously aware that some suspicions had been at 

 different times entertained that the changes of azimuth, as ob- 

 served with the transit instruments employed in the observatories 

 of Greenwich, Edinburgh, and Trivandrum, were periodic ; yet 

 my attention was especially drawn to the subject by the singular 

 fluctuations in the errors of level and azimuth, which I have 

 remarked since the Sydney Observatory came under my direction. 

 Now I am compelled to admit, that although I think I have de- 

 tected something like a periodicity in these fluctuations, yet they 

 are not sufficiently regular to draw any decided conclusions 

 from them taken by themselves. And we cannot be surprised at 

 this when we consider the position of the present observatory. 

 Bounded, as it is, on three sides by precipitous rocks, at distances 

 varying from one to three hundred feet long ; and the hill itself 

 composed of material which peculiarly ttnfits it for an Ob- 

 servatory ; so that there are continual displacements of the com- 

 ponent parts, of such magnitude as to prevent the detection of 

 those subtle changes which result from the regular laws of nature. 

 Moreover, since the erection of the observatory, the stability of 

 the hill has been still further endangered by the excavation of 

 stone from the sides ; and on such occasions sudden and irregular 

 instrumental changes have been observed, which could be ac- 

 counted for on no other supposition. 



Still impressed with the conviction that such periodic 

 changes do occur as must be traced to regular Geological laws, 

 and not to accidental circumstances, I selected for my investiga- 

 tions the Royal Observatory of Greenwich, and I need hardly 

 comment upon the importance of such selection. Situated upon 

 a well selected soil in the midst of Greenwich Park, and kept 

 free, by legal enactment, from any disturbances such as roads or 

 railways or indeed anything which might produce the slightest 

 vibration ; with the ." Astronomer Royal " for England as its 

 Director, and a large and highly efficient staff ; with instruments, 

 the best that art and money could procure, we may be satisfied 

 that even the shadow of doubt cannot rest upon the observations 

 made and reduced there. 



