Intelligence and Miscellaneous Articles. 235 



ticularly applicable to that purpose, as well as to the measurement 

 of any elevation where a barometer can be employed. 



I procured a straight barometer-tube thirty-three inches in length, 

 and also a bottle one inch in diameter, and the same in depth. In 

 one side of this bottle, near the top, I bored a small hole ; and hav- 

 ing filled the tube with mercury, and the bottle rather more than 

 half full, I inserted and cemented the tube into the neck of the bot- 

 tle, with its open end a little below the middle ; so that in every po- 

 sition the opening was covered with mercury. 



I then fitted the whole into a casing of wood, the tube, for twenty- 

 five inches of its length, being imbedded level with the surface ; the 

 upper end opposite the scale, for the length of eight inches, being 

 fully exposed. The divisions of the scale denoting inches and 

 tenths, are reduced a little, to compensate for the variation of the 

 surface of the mercury in the cistern. For a vernier, I took a very 

 thin piece of silver, the length of eleven divisions of the scale, and 

 breadth something more than half the circumference of the tube ; 

 this divided into ten parts by lines quite across, except a small 

 space for the figures, and bent so as to embrace the tube with a 

 gentle elastic pressure, is made to slide as freely as required : the 

 lines of the scale being reflected from the surface of the silver, af- 

 ford great assistance in observing the coincidence, dividing the inch 

 very accurately into an hundred parts ; and a figure in the third 

 place of decimals may be estimated by the eye. The lower part of 

 the case being secured by a piece of thin brass plate, with a bottom 

 projecting in front beyond the diameter of the bottle, I fit a wooden 

 cover, the whole length of the instrument, with two pins to pass 

 into corresponding holes in the bottom-plate : a bit of soft leather is 

 placed so as to press on the mouth of the hole in the bottle, and 

 the case being made a little taper, is easily kept close by a slight 

 hoop of leather. 



This barometer, with a moderate degree of precaution, is suffici- 

 ently portable, and very ready in use ; it requires no other prepa- 

 ration for an observation than merely to hang it perpendicularly, and 

 take off the cover ; the air having immediate access to the surface 

 of the mercury in the cistern, renders it more satisfactory than those 

 in which it has to pass through the pores of the wood, and where 

 the surface of the mercury cannot be seen ; and less troublesome 

 in use, with less risk of error, than others, in which it has to be ad- 

 justed by a screw for every observation. 



If a due proportion is attained in the divisions of the scale, and 

 proper attention paid in taking a mean observation at each station, 

 to obviate the effects of the friction unavoidable in small tubes, I 

 am convinced that it will be found as accurate as any barometer of 

 the same dimensions, although of a far more elaborate and expen- 

 sive construction. 



Keswick, Aug. 7th, 1828. I am, &c. J. Otley. 



NUMMULITES IN THE GREEN-SAND FORMATION. 



In a note inserted in the third volume of the Memoires dc la 



2 H 2 Societe 



