Cotswold Hills, with observations on the Aneroid Barometer. 41 



Throwing out of consideration, then, some of my first trials, 

 before I was quite up to the use of the instrument and its tables, 

 the results which I have just given are highly satisfactory. But 

 on the other hand I tried it against the published sections of the 

 Cheltenham and Great Western Railway with less success, as the 

 following comparison will show : — 



By Company's By Aneroid. Krror. 

 sections. 

 fss*. feet. feet. 



Stmud station above Gloucester station 116-3 124*75 +8*45 



Summit-level at top of Saperton tun- "I 350-0 413*7 4-61-5 



nel above Gloucester J 



Now these were the means of two trials ; in the latter case 

 the discrepancy is greater than I can easily explain, unless the 

 oscillations of the railway carriage have any effect on the instru- 

 ment, which I can hardly suspect ; for in all other cases, however 

 carefully carried, it must have been exposed to rough shaking*. 

 On the whole therefore I must suspend my opinion as to the 

 merits of the aneroid for measuring heights till after further ex- 

 periments, and at any rate would recommend the improvements 

 in the construction, to which I have before alluded, to be effected, 

 viz. the decimal graduation to be adopted, and the index to be 

 placed closer to the face of the instrument. 



P.S. Since the compilation of the above paper I have been 

 fortunate enough, on a visit to Paris, to make the acquaintance 

 of the ingenious inventor of the aneroid — which I find, in its 

 present state, he regards as a domestic rather than a scientific 

 instrument, — an estimate of its capabilities in which its continued 

 use leads me very much to concur. Still, while I find it per- 

 fectly well adapted to the house purposes of a common weather- 

 glass, I can say no less of it as an instrument for taking heights, 

 than that it is far more commodious and much less likely to get 

 out of order than a mercurial barometer — and when limited, as 

 my trials were, to heights not exceeding 1200 feet, that it 

 exhibits quite sufficient accuracy for general purposes — a power 

 which I have no doubt in its present form may be extended to 

 heights of some 2500, and were the index graduated to 24 or 25 

 inches of the mercurial barometer, probably to the height of any 

 hills in Great Britain. 



M. Vidi, however, has made some elaborate trials towards a 

 more purely scientific instrument. If he persevere, I have no 

 doubt he will succeed. 



The grand Exhibition of Works of Art in London in 1851, 

 offers him a good opportunity for submitting his invention to more 

 general notice, — and, to the judges perhaps, a not inappropriate 

 object for a premium. — W. II. II. 



* The error may be this — that the Company's sections were published 

 before the completion ot' their line, which was eventually carried at a rather 

 higher level than these sections 1 



