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Subsection of Mechanical Sciences applied to the Arts. 67 
On the Monthly Reports of the Duty of Steam-engines employed in 
draining the Mines of Cornwall. By Joun Tay or, F.RS., 
Treasurer of the British Association. 
Mr. Taylor observed that he had found at this and other Meetings 
of the Association considerable interest to be expressed with regard 
to this method of recording the actual effect produced by the con- 
sumption of a given quantity of fuel, and recommended it to the 
notice of engineers in general. ‘The monthly reports alluded to gave 
the means of comparing one engine with another in this district; 
they also afforded an historical view of the progress of improvement 
in this important machine; and they had, Mr. Taylor believed, 
contributed largely to that improvement, by the emulation and at- 
tention excited by them in the persons who had the charge of con- 
structing and managing the engines. 
Mr. Taylor stated that the work done in the best engines now 
employed in Cornwall by the consumption of one bushel of coal, re- 
quired ten or twelve years ago the consumption of two bushels ; 
that during the period of Boulton and Watt’s patent four bushels 
were consumed to do the same work, and that in the earlier stages of 
the employment of steam power the quantity of coal used was 16 
bushels, So that by the progressive advance of improvement one 
bushel had become sufficient for the ‘duty that formerly required 
sixteen. 
Mr. Taylor, in remarking on the importance of this subject to the 
deep mines of Cornwall, stated, that the steam-engines now at work 
for the purpose of draining the mines there were equal i in power to 
at least 44,000 horses, and that as some doubts had frequently been 
expressed as to the accuracy of the results shown by the duty re- 
ports, he had compared them some time since with the accounts 
of the coal actually used in some of the principal mines at different 
periods, by which he found the saving of money was as great as the 
reports indicated, and that their general accuracy was borne out 
fully by the account books, where this was incontestably proved. 
Description of a Self-registering Barometer 5c. By Prof. StEVELLY. 
During the oscillations of the common barometer, when it falls, a 
certain quantity of mercury is added to that already in the cistern, 
which of course adds so much to its weight; on the contrary, when 
it rises, mercury retires from the cistern, which thereby becomes so 
much lighter than before. If, then, the tube of a barometer be fixed 
firmly in its place, but the cistern be by any means so suspended as 
to move downwards by equal distances for equal additions to its 
weight, and to rise similarly for similar diminutions of its weight, it 
is clear that a scale may be placed beside the cistern; and an index 
carried by the cistern may be made to mark upon the scale a 
variety of positions corresponding to the rising and falling of the 
common barometer. It may be shown to any person even slightly 
conversant with mathematical subjects, that the range of this scale 
may be made to bear any proportion to that of the common baro- 
meter. Supposing for an instant what is now stated to be accom- 
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