64 



REPORT OF THE SECRETARY. 



The lines of development have been: (1) In the increase of delicacy ; (2) in the 

 increase of stability and accuracy. 



With a \ iew to increased delicacy much time has beeu devoted through the year 

 to the improvement of the galvanometer. 



During the absence, in Europe of the present senior assistant, he, by my direction, 

 devoted two weeks exclusively to this work, and the elements of three galvanometers 

 were constructed after his design, two by Nalder Bros, and one by Elliott Bros. 

 After his return, the work of improvement of my earlier designs for the old galvan- 

 ometer and of the new ones was at once begun. Pending the completion of the new 

 galvanometers, the improvement of the three old ones already in use was undertaken, 

 and the delicacy of each was more than doubled. Up to date only one of the new 

 galvanometers has been completed, and this owing to the introduction of an almost 

 unprecedcntedly light, magnetic system, and through other improvements, has been 

 found to be about 35 times more delicate than the best of these previously in use. 



This degree of delicacy will, it is probable, be exceeded by one of the two remain- 

 ing forms, but lack of time has prevented further improvement at present. Indeed 

 the conditions of use at present are such as to render ouly about one-tenth of this 

 increased delicacy available, and only a new laboratory will enable the full increase 

 of delicacy to be perfectly utilized. 



An abbreviated statement of the galvanometer work for the year is appended: 



Galvanometer. 



(Old) D'Arsonval 



White (old) Alleghany pattern Thomson 



Queen (old) do 



Elliott Bros. spe< nil design new do 



Nalder Bros, special design new , Thomson (multiple)t- 



Do D' Arson val 



Old constant.* 



-000000 10000 

 -00000000150 



0-00000000160 



New constant 



(alter improve- 

 ment). 



•00000002000 



•00000000070 

 •00000000040 

 (10000000004 

 •00000000002 

 Not finished. 



K Current which deflects iniaj 

 vitiation is 10 seconds, 

 i Partially finished. 



;e one millimetre at distance of 1 metre, when the time of a single 



For use in these new galvanometers, the laboratory has received during the year. 

 a lot of very fine quartz fibers, made to special order by Prof. C. C. Hutchins, and 

 some very small, light, and accurate concave mirrors from J. A. Brashear, the use of 

 which in the new galvanometer has been already referred to. A very considerable 

 improvement in the mechanical steadiness of this part of the apparatus has also been 

 effected by mounting the whole galvanometer in a massive metal case, which rests 

 on a series of stone blocks placed one above another and separated from each other 

 by sheets of rubber. In spite of these precautions, the vibrations due to passing 

 teams and wagons are at times still very troublesome. 



(2) The improvement in the other parts of the apparatus has been mainly in the 

 direction of increased accuracy. The siderostat has been provided with a new elec- 

 tric control, by means of which inaccuracies of running may be quickly compensated 

 for from inside the building. Considerable improvement has also been effected in 

 the minor parts of the instrument, but it still needs to be thoroughly overhauled. 

 The changes for which there is most pressing need are the remounting of the 

 equatorial axis on ballbearings ami the construction of a new governor for the clock. 



The spectro-bolomctcr and its accessories is that part of the train of apparatus 

 which has undergone the most radical change. The principal changes which have 

 been made in its construction and working during the past year are: 



(1) The adoption of a reflecting mirror secured to the prism and revolving with 

 it, which has rendered it possible to fix both the spectro-bolometer slit and the 

 bolometer itself in position, thereby avoiding the use of a long revolving arm. 



