1841.] On the Salts, called Puckwah and Phool-Kharee. 957 



by the use of the test, which thus becomes in all probability as good 

 a one for the adulteration by Puckwah as for that practised by means 

 of the Kharee. 



Calcutta, Zlst October, 1841. 



Remarksby Captain J. T. Boileau, Bengal Engineers, F. R. S., F. R. 

 H. S., on the construction of Newman^ s improved Portable Baro- 

 meter, and on the mode of renewing the Gauge Point when lost ; with a 

 Drawing. 



A recent modification has been made in the portable (or as it is 

 more commonly called the mountain) Barometer, by Mr. Newman of 

 Regent Street, London, whose standard Barometers have become so 

 justly celebrated; and believing that a description of these instruments 

 has not yet been published in India, I am induced to forward the ac- 

 companying sketch of their construction, and at the same time annex 

 the result of some comparisons made with two of these portable instru- 

 ments, and the Observatory standard, for the purpose of determining the 

 gauge (or neutral) point of the latter, which had been lost in both by 

 the escape of a considerable portion of mercury from their cisterns. 



In the best portable Barometer of Troughton, Dollond, and Gary, the 

 surface of the mercury in their cistern is brought by a simple mechani- 

 cal contrivance to the level of a gauge point, (the Zero of the divided 

 scale ; by which the height of the column is read,) a measure of which 

 if the gauge point were invariable, would do away with the necessity for 

 a correction on account of the varying height of the mercury in the 

 cistern, due to the rise and fall in the column. 



The gauge point, or line, is not however invariable in either of the 

 above constructions save Gary's ; and Mr. Newman's object appears to 

 have been to devise an instrument, which should be independent of the 

 adjustment, preliminary and essential to each observation in those of 

 the above kind, and whence the true height of the mercurial column 

 should yet be deducible with as much accuracy, as if it had been read 

 from the absolute Zero of the scale. 



It is in the construction of its cistern that Newman's portable 

 Barometer differs chiefly from others, and a description of this part, 

 therefore, is all that is essential. 



