960 NewmarCs improved Portable Barometer^ S$c. [No. 120. 



meter, and thus improved, it would be found one of the most convenient, 

 safe, and elegant instruments of its kind ever made, instead of being, 

 as it now is, an almost useless toy. 



In proof of this assertion, it is only necessary to mention, that 

 both the portable Barometers brought out as a part of the equipment 

 of the Simla Magnetic Observatory, were found to be quite unservice- 

 able the very first time they were taken out for use ; the mahogany 

 tube was loose in the brass case of the cistern, and in one, (No. 44,) 

 had warped, so as to have broken the Thermometer ; in both, the box- 

 wood cap, which attaches the glass tube to the cistern had shrunk, 

 so that the mercury escaped in large quantities, and the neutral point 

 being thus lost, the Barometer was of course, in its present state, useless 

 for absolute measurements ; but having no other instruments, it became 

 an object of importance to repair, if possible, those in my possession, 

 and to institute a gauge point or neutral reading for them by compari- 

 son with the standard in the Observatory, and I am induced to forward 

 an account of the method in which this has been effected more pour 

 encourager les autres, who may be left to their own resources as I have 

 been, not to set aside even an imperfect instrument without an effort to 

 improve its condition : for the result of my own attempt has certainly 

 proved as successful as, under the circumstances, could have been ex- 

 pected. It is of the first importance too, in the publication of altitudes 

 determined by the Barometer, that the quality of the instrument em- 

 ployed should be known, and as the two portable Barometers in my 

 possession will be used frequently for determining the relative heights 

 of mountains by simultaneous comparisons with the standard in the 

 fixed Observatory, the following details are the more necessary, as shew- 

 ing what weight may be attached to the observations made with them. 



The first thing necessary was to make the cistern perfectly mercury- 

 light, which has been completely effected by a stuffing of tow and glue 

 round the boxwood cap, the cap having been filed to a level (inwards) 

 sufficiently to allow of a wrapper of the above materials being applied and 

 pressed down by an iron tool from above — next, the instrument being 

 inverted, a hole (ef) bored in the lower chamber and a fine screw tapped 

 into it ; a supply of mercury was then introduced, and the cistern being 

 screwed up, the instrument was set by to dry for some days, after which, 

 the comparisons for determining the neutral reading were commenced. 



