230 SCIENTIFIC NEWS. 



Kralzcnstein has given same account of the principles of an 

 engine of this kind in a memoir extracted in the Journal de 

 Physique, and Dr. Young has cursorily mentioned the subject tfl 

 his lectures, with some diagrams. 



Quantity of Spirits and other fluids ascertained ly Weight. 



Mrs. Lovr has lately communicated a memoir to the Edin- 

 burgh Institute, upon the advantages in point of accuracy of 

 measuring fluids by weight instead of using vessels of known 

 magnitude. She is mentioned as patentee of the areometricai 

 beads, which have been now upon sale in London for a con- 

 siderable number of years, and consist of small glass balls 

 hermetically scaled, having their specific gravities written upon 

 them. The principal objection to these is their number and 

 brittleness, and, perhaps, the difficulty of making them of so 

 small a size, with as much accuracy as the larger ball, of the 

 usual floating instrument. 



With regard to the practice recommended of weighing fluids 

 instead of measuring them, it is grounded on the considerations, 

 I. That weights are usually made with more exactness than 

 measures. 2 The measuring multiplies error by aseriesof operations, 

 3. and it has been questioned whether a single measure of a 

 fluid could be had to the same degree of precision as a mass 

 determined by weight j though by the common figure given 

 to the copper measures which terminate in a neck or throat 

 having a small surface, the precision required in business may, 

 no doubt, be had. — Considerations of temperature affect both 

 methods alike, and I apprehend that, though the temperature of 

 spirits is attended to, in determining their strength, yet it is 

 neglected in taking the measures of quantity j which it is liable 

 to affect as far as 2 per cent, or one gallon in 50, and ought, 

 therefore, to be considered. 



I have seen oil sold retail by the gallon weight in London, 

 which is certainly very fair for the buyer, who might else in 

 that adhesive fluid, lose as much as hangs to the vessel every 

 time it is emptied. . 



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