306 Self-Registering and Indestructable Barometer* [April 



VII. — Remarks upon the Plans proposed for Constructing a " Self-Re- 

 gistering" and an " Indestructable" Barometer. — By T. G. Taylor, 

 Esq. of the -Madras Observatory. 



In the January No. of the Madras Journal of Literature and Sciences, 

 some attempt has been made to meet the present wants of the meteo- 

 rologist, by supplying him with a barometer which promises to be " in- 

 destructable," or, in other words, one which is little liable to get out of 

 order with ordinary rough usage ; and in the same No. of the Journal, 

 a further attempt at meteorological improvement is made, in the way of 

 a self-registering barometer. That an indestructable barometer is 

 much wanted, is a fact but too well known to every one who has used 

 the ordinary instrument for any length of time on a march or even at a 

 fixed residence; and the importance of a self -registering barometer is 

 such, as to render any attempt at its accomplishment a matter of inter- 

 est. With this view of the subject, and considering that the plans pro- 

 posed for both of the above purposes are more or less true in theory,, I 

 have thought it may not be unacceptable to offer a few remarks rela<- 

 tive to their practical utility. 



In the first place it must be noticed with regard to both of these 

 plans, that the employment of a metallic tube is highly objectionable,, 

 by reason of the little dependence which can be placed in it, to main- 

 tain a perfect vacuum for any length of time, even for a day -.—not to 

 offer an opinion gratuitously, however, I may mention the experience 

 of Captain Sabine, of the royal artillery. Captain Sabine, requiring 

 an air-tight apparatus, employed Mr. Newman, the justly celebrated 

 and careful philosophical instrument maker. Mr. Newman, fully aware 

 that cast-iron could not be trusted, employed gun metal, and that too of 

 three-quarters of an inch in thickness. The gun metal failed ; and an 

 air-tight apparatus was only obtained at length, by covering it on both 

 sides with three coats of paint. In addition to this, and bearing more 

 immediately on the point in question, I may state, that a barometer, 

 constructed upon the " indestructable" plan, has lately been subjected 

 to trial at the Madras Observatory. The tube was made out of a well 

 twisted London-made gun barrel ; this of itself proved unequal to ex- 

 clude air, but was afterwards made tight by a coating of caoutchouc 

 varnish — a precaution, however, which was eventually of no avail, for, 

 on the application of fire, for the purpose of boiling the quicksilver in 

 the tube, the leakage recommenced, so that nothing further could be 

 done with it. 



With regard to the self-registering barometer,, the idea is certainly, 

 at first sight, a very pretty one, and, but for the metallic tube, appa- 

 rently unobjectionable. Since, however, a metallic tube is not abso- 

 lutely necessary, we will take the liberty of introducing in its stead a 



