1^ REPORT ON THE COMPLETION OF 



apparatus being placed horizontal and the agate planes being removed, adjust a 

 telescope so as to read the scale, and turn the ciicle, &c., round, so that a given 

 division shall occupy different azimuths ; then from the variations of scale read- 

 ing (the changes of declination being subducted), the effect of the circle, &cc., 

 upon the needle in different positions is determined ; and from these the effect 

 upon the needle, when the whole apparatus is vertical, may be easily obtained. 

 This process will be found much more satisfactory then than that by vibrations. 

 I would only farther suggest, that the process should be repeated, with the poles 

 changed, and that the position of the needle should be obtained for the appara- 

 tus away ; shice in some needles I have found that the intensity of saturation dif- 

 fers with the end which is made north, and that one end is sometimes much 

 weaker than the other. 



The Horizontal Force-Measu7'er. — For a fixed observatory, I feel inclined to 

 prefer thin parallelopipedal magnets, perhaps about 8 inches long, with deflections 

 of from 3° to 8° according to M. Gauss's method, rather than the small magnets 

 and large deflections by Dr Lamont's. If, however, the 4-inch magnets are used I 

 prefer a modification of Dr Lamont's method which Dr Lloyd has employed, in 

 which the deflecting bar is kept always at right angles, not to the suspended mag- 

 net, but to the magnetic meridian. This subject requires considerable examina- 

 tion ; the discordant results obtained from different instruments, and from the same 

 instrument with different magnets, are too considerable not to require explana- 

 tion. The deflecting magnet should never be touched with the hand during ob- 

 servations, but it should be lifted by a carriage or chair. The expansion of the 

 distance beam should not be omitted in the computation of the absolute inten- 

 sity ; where it is of brass the effect of this omission may be quite marked in com- 

 paring observations during summer and during winter. I may touch upon the 

 whole subject again in another way. 



Having noticed those points which have occurred to me as of principal im- 

 portance, or as more or less new, I cannot conclude this report without adverting 

 to the assistance which 1 have received from different gentlemen during my labours 

 at Makerstoun. 



To yourself I have been especially indebted. The foundation and support 

 of the observatory is a thing, of itself, which might be noticed as a matter 

 for gi'atulation. It is rare for persons with much more extensive means to 

 have done so much for science, — while they were themselves living and capable 

 of otherwise employing their wealth — it is rare for them to have done so much 

 even by their bequests. This reason for thanks I possess only in common w^ith 

 other lovers of science. It is for your personal kindness, the friendship with which 

 you have honoured me, the suggestions and aids which I have derived from you 



