On Gravimeters. 



535 



At this point, I decided on abandoning the investigation, nntil I 

 should receive further instructions. . Considering that the instrument 

 has been entrusted to me to experiment with rather than upon, I have 

 already dared more perhaps than I ought to have — certainly more 

 than most persons would have felt justified in doing. I presume, per- 

 haps, in thinking that a rather long experience of instruments of 

 precision will be accepted as my excuse for having gone so far ; in the 

 earnest endeavour to ascertain whether an instrument of such exceed- 

 ing beauty (as to workmanship) would prove as valuable as it looked, 

 and as, I must say, the principle of its construction leads one to 

 expect. In pursuing this endeavour I have done some slight injury 

 to it — which can be easily remedied if necessary. This I admit : but 

 per contra I have ascertained a good deal without which it would be 

 useless, besides gaining some experience which should avail in per- 

 fecting it, and making it (or another similar in principle) useful for 

 its intended purpose. Finally, if any further apology is necessary, I 

 will add this — that in no case could the instrument have been actually 

 and efficiently employed for that purpose without material alterations. 



I cannot too often repeat, that both as regards the design and its 

 execution, the instrument deserves high praise. Nevertheless it is a 

 failure. I have felt this all along, and I ought not to conclude this 

 paper without pointing out what I conceive to be its chief defects. 

 Of the defect which has brought this trial to a premature conclusion 

 — the insufficient hold of the ends of the wires — it is only necessary 

 to say that some plan should be discovered of putting this beyond 

 question. This is the first consideration. I do not regard this as an 

 error either of design or of construction such as can be complained of. 

 But I do regard as such that which gives the instrument, as actually 

 constructed, its beauty, viz., the minuteness and delicacy of its parts. 

 There is a wealth of adjustment which is not necessary, and their 

 details are all on far too small a scale. I suppose that the major 

 weight consists of not less than 100 parts. Of these probably 80 

 could be set apart whose total weight would not reach 200 grs. out 

 of the 3,100 which the whole weighs. It is clear that, supposing the 

 total to be restricted to that, a more generous distribution to the 

 smaller parts might have been made, without any disadvantage ; but 

 on the contrary, a great gain in handiness. I fear it is useless to add 

 that a large proportion of these smaller parts are of the kind which 

 instrument makers delight to show their wonderful skill in producing 

 — as nature does flowers. Of course, one cannot tell how far these 

 multifarious adjustments may not owe their presence to a conscientious 

 endeavour on the part of the maker to give effect to his instructions : 

 but that must not prevent my saying that they are, to a large extent, 

 redundant, unnecessary, if not useless. 



I regard it as a mistake that the whole instrument is on so small a 



