518 



Major J. Hf3rschel. 



the factor is reduced to g-ooVo'o* seems highly probable, how- 

 ever, that the residual effect would no longer be a simple function of 

 the change of temperature, and might be quite incalculable. 



It is also necessary to consider that the masses of metal concerned 

 would probably, except under controlling conditions, cause consider- 

 able uncertainty in this effect. 



Enough has been said to show that the bathometer, although a 

 gravimeter in principle, cannot be regarded as likely to prove of ser- 

 vice in measuring small changes of gravity under different climates. 

 Its efficacy as an instrument for measuring sea-depths need not be 

 considered here. It may have peculiar properties in that connexion 

 which I have not understood ; for indeed I may confess a certain 

 hesitation in believing that any instrument can do that, by deter- 

 mining the change of attraction, except under conditions favouring an 

 empirically deduced scale. 



There are rumours of other designs for measuring small changes of 

 gravity, of quite recent invention, of which I can only say at present 

 that it is very much to be hoped that they will serve their intended 

 purpose, and that we shall soon be in possession of experimental 

 evidence to that effect. 



II. On the Torsion Gravimeter, constructed on the Design of the late 

 J. Allan Broun, by Br. G. 8. Miiller, of Stuttgart. 



Before entering upon any description of this instrument it may be 

 w^ell to explain that the title of this paper is intended to take cogni- 

 zance of the fact that the designer did not experiment with it or 

 improve upon it after it left the maker's hands, and that consequently 

 some portion of the merit, whatever it may prove to be, is due to the 

 appreciation of the design by the latter. Conversely, it is due to the 

 designer to recognise that failure of any kind may to some extent be 

 attributable to misapprehension on the part of the maker. At the 

 same time, it must be said that the workmanship is of a high order, 

 and betokens a more than ordinary attention as well as great skill 

 and delicacy. Should the instrument justify its existence by its 

 ultimate utility, it cannot be denied that it will owe its success, in a 

 high degree, to the intelligence of the constructor as well as to the 

 genius of the inventor. 



There are two ways of describing a new form of instrument. We 

 may either approach it from outside, and learn its functions by con- 

 sidering its parts, or we may study it with a prior knowledge of its 

 intention. The latter method is, perhaps, the best for one to adopt 

 who wishes to describe an instrument of his own designing ; for he 

 cannot fail to indicate truly what design he had. But for one whose 

 only knowledge of the functions of an instrument are inferred from 

 what he sees, it might be dangerous to presume a full knowledge of 



