94 Mr. H. Russell's Description of a Pressure Gauge. 



gauge complete (except that there are given only the geome- 

 trical divisions) with the mercury chamber blown in the 

 tube itself; so that on this plan we have no joints whatever 

 to make in the instrument : and being placed in a horizontal 

 position at a convenient distance from the floor, all parts of 

 the scale may be examined with equal facility. 



For the internal diameter of the tube, perhaps y^-th of an 

 inch will be found preferable. 



The following numbers represent, in inches and decimal 

 parts, the spaces between each division representing a num- 

 ber of atmospheres and the top of the scale. 



Atmospheres. Inches. Atmospheres. Inches. 



1 = 96-000 17 = 5-647 



2 = 48-000 18 = 5-333 



3 = 32-000 19 = 5-052 



4 = 24-000 20 = 4-800 



5 = 19-200 21 = 4-571 



6 = 16-000 22 = 4-368 



7 = 13-714 23 = 4-173 



8 = 12-000 24 = 4-000 



9 = 10-666 25 = 3-840 



10 = 9-600 26 = 3-692 



11 = 8-727 27 = 3-555 



12 = 8-000 28 = 3-428 



13 = 7-384 29 = 3-310 



14 = 6-857 30 = 3-200 



15 = 6-400 31 = 3-096 



16 = 6-000 32 = 3-000 



I shall now endeavour to point out to you, that the gauge 

 proposed by Mr. Seaward is not so good an instrument as 

 the one in common use, upon which he seems to think that he 

 has made so much improvement. The first article in what 

 Mr. Seaward calls his description runs thus : " Considerable 

 difficulty has been experienced in ascertaining in a satisfactory 

 manner the exact pressure of highly condensed gases or fluids." 

 Now I would ask Mr. Seaward, where has he met with this 

 difficulty ? or, how can we possibly meet with any difficulty 

 when guided by an instrument of perfect simplicity, as is the 

 pressure gauge in common use? He knows what the com- 

 mon pressure gauge is, for he clearly describes it. 



He next says, " But it happens that when fluids are re- 

 quired to be compressed to 30 or 40 atmospheres, it becomes 

 necessary to have the tube of the mercury gauge of very great 

 length, say from 30 to 45 feet, otherwise the divisions of the 

 upper part of the scale will be much too small for useful re- 

 ference." How far Mr. Seaward is justified in this assertion, 



I leave 



