380 



Dr. O.-Chree. Collimator Magnets and, the 



recorded value of the angle through which the magnet deflected an 

 auxiliary magnet at a distance of 1 foot, that being a quantity deter- 

 mined in the induction experiment. Old magnets, when remagnetized 

 and retested, have been treated as new magnets and counted separately. 



§ 7. The discussion of Tables I and II would have been much simpli- 

 fied if one had possessed a record of the weight and dimensions of the 

 collimator magnets themselves. It is not, however, customary to 

 measure these quantities at the Observatory, as they in no way enter, 

 into the tables used in reducing the observations. 



The only data at my disposal, bearing directly on these points, are 

 the results of special measurements recently made on six magnets, 

 three belonging to group C, and three to group E. 



The results were as follows, the numbering being purely arbitrary ; 

 the lengths are in centimetres, the weights in grams : — 



Table III. — Dimensions and Weights of specimen Magnets. 



Gi-roup. 



Magnet. 



Length. 



External 

 diameter. 



Internal 

 diameter 

 at end. 



Weight 

 magnet. 



Weight 

 append- 

 ages. 







cm. 



cm. 



cm. 



grams. 



grams. 





i 



9*36 



1-00 



0-81 



27 -33 





•i 



ii 



9 30 



1-00 



0-80 



28-11 







iii 



9*30 



1-00 



0-80 



30 '20 



26-28 





Mean 



9-32 



1-00 



0-80 



28 '55 







iv 



9-18 



1-055 



0-815 



25 -21 







y 



9-12 



1-055 



0-815 



25 -64 







vi 



9*13 



1-03 



0-80 



26-02 



32 -41 





Mean 



9'14 



1 -05 



0-81 



25-62 





The specific gravities found for two of the magnets were approxi- 

 mately equal, the mean being 7*67. 



From this we conclude that in both groups of magnets the wall 

 thickness is less at the extreme ends, where an internal screw is cut, 

 than elsewhere; the mean internal diameter deduced from the data 

 being 0-70 cm. for the magnets of group 0, and 0*77 cm. for those of 

 group E. The actual volumes of steel in the two cases were respec- 

 tively 3-72 and 3'34 c.c. 



There has been but little variability in the length or external 

 diameter of the magnets of any one group • the volume however, if we 

 may judge by Table III, is somewhat more variable. We should have 

 more exact information on the point if K meant the moment of the 

 magnet alone, but as matters stand, our conclusions are exposed to some 

 uncertainty. The appendages, as we see from Table III, weigh about 

 as much as the magnets themselves,' their main mass lies however 

 nearer to the axis of rotation. In fact, according to the measurements 



