393 



last two years, it is most probable that the disruption of these masses 

 of ice from the place of their formation was the effect of some pow- 

 erful cause of rare occurrence, such as an earthquake or volcano, 

 which has burst forth and convulsed the inaccessible regions of the 

 south ; leaving no other testimonials of the event, than some few 

 fragments of ice, scattered at a distance in the Indian Ocean. 



On the progressive Improvements made in the Efficiency of Steam En- 

 gines in Cornwall ; with Investigations of the Methods best adapted 

 for imparting great angular Velocities. By Davies Gilbert, Esq. 

 P.R.S. Read March 4, 1830. [Phil. Trans. 1830, p. 121.] 



The practical adaptation of the steam-engine to mechanical pur- 

 poses is considered by the author as due to Mr. Newcomen, whose 

 engines were introduced into Cornwall very early in the last cen- 

 tury, and soon superseded the rude machinery which had till then 

 been employed for raising water from the mines by the labour of 

 men and of horses. The terms proposed by Mr. Watt, in virtue of 

 his patent in 1769, which secured to him, until the year 1800, the 

 receipts of one third of all the savings in fuel resulting from the adop- 

 tion of his improvements in the construction of the engine, rendered 

 it necessary to institute an accurate comparison between the ef- 

 ficiency of his with former engines. A copy of the report drawn up 

 on this occasion, in October 1778, is given in the paper; but as the 

 dynamic unit of one pound avoirdupois, raised through a height of one 

 foot, had not yet been established as the measure of efficiency, the 

 author, proceeding upon the data furnished by that report, calculates 

 that the duty performed by Watt's engine, with the consumption of 

 one bushel of coal, on that occasion was 7,037,800. In the year 

 1793, an account was taken of the work performed by seventeen 

 engines on Mr. Watt's construction, then working in Cornwall, their 

 average duty was 19,569,000 ; which exceeds the performance of the 

 former atmospheric engines, in the standard experiments, in the pro- 

 portion of 2*78 to 1. Some years afterwards, disputes having arisen 

 as to the real performance of Mr. Watt's engines, the matter was re- 

 ferred to five arbiters, of whom the author was one ; and their report, 

 dated in May 1798, is given as far as relates to the duties of the en- 

 gines. The general average of twenty-three engines was 17,671 ,000. 

 Since that period, so great have been the improvements in the eco- 

 nomy of fuel and other parts of the machinery, that in December 

 1829, the duty of the best engine, with a cylinder of 80 inches, was 

 75,628,000, exceeding the duty performed in 1795, in the proportion 

 of 3'865 to 1 ; and that of the atmospheric engine of 1778, in the 

 proportion of 10' 7 5 to 1. 



The remainder of the paper relates to the friction in machinery, 

 and the different modes of obviating its effects. With a view of re- 

 ducing the amount of friction, the author is led to consider what are 

 the most proper forms for the teeth and cogs of wheels ; and through 

 what intermediate steps a given increase of angular velocity may be 



