1 06 Remarks on Mr. Hume's Gazometcr and Blow-pipe. 



104= 30', gives the true distance 103° 57' 34". But should the 

 perpendiculars cut to the left of the seniidiameter, the sum mul- 

 tiplied by the horizontal parallax must be divided by 52; and 

 then the correction is to be added to the apparent distance^ to 

 find the true distance. 



N. B. This instrament may be made either in brass, wood, or 

 with care in card. I made a model in card, with a radius of 

 about six inches, which gave the true distance within 10' or 

 15" of it when worked by other methods. 



XIX. Remarks on Mr. Hume's Gazometer and Blow-pipe. 



By a CoRRESrONDENT. 



To Mr. TiUoch. 



U London, AuEust 13, 1814. 



PON reading in your Journal for the preceding month, a 

 paper by Mr. Hume, wherein he describes a method for con- 

 structing an improved blow-pipe, out of some chemical appa- 

 ratus, possessing the peculiar advantage of yielding a current 

 of atmoispheric air by inhalation ; a suggestion occurred to me, 

 which upon trial was verified, that too great exertion of the 

 lungs would be required to render the current of air of suffi- 

 cient duration to be useful in chemical or mineralogical experi- 

 ments. 



The VVoulfe's bottle I used for this purpose contained about 

 three pints; and though it required considerable exertion to draw 

 up the water inlo the separating funnel, yet the stream of air 

 continued onlv three-quarters of a miimte ; a time certainly in- 

 sufficient to make scarcely any experiment. 



Nmv I am inclined to tiiink that the cjlindric gazometer, 

 which is almo5,t indispensable to the chemist, and is frequently 

 used for this purpose, answers the end proposed by Mr. Hume 

 more completely than his contrivance; because, merely by raising 

 the interior cylindrical vessel, as many cubic feet of atmospheric 

 air mav be obtained in a given time, as by inhalation we could 

 obtain inches; and with this additional advantage, that the force 

 of the current of air may be increased or decreased at pleasure. 

 Nevertheless, I think that Mr. Hume deserves great credit for en- 

 deavouring to increase the powers of the philosophical chemist, 

 without increasing his app'^ratus, the expense of which already 

 deters many from the pursuit of so pleasing and useful a science. 

 I am, sir, 

 -: Your most obedient servant, 



W. W. 



XX. Me- 



