Mechanical Science. 150 



into the lead at each time of pouring. To ascertain the truth of 

 this opinion, a stopcock was attached to the bottom of the melting 

 vessel so that the lead could be drawn off without any contact with 

 the atmosphere, the surface above being covered all the time with 

 a thick layer of charcoal powder. Then the former experiments 

 being repeated, it was found that lead, after the first fusion, was 

 reduced to 303, less than on any former occasion ; after a second, 

 to 311 ; and, after a third, to 301 ; so that now no repetition effusion 

 produced any effect. Some of the lead was also cast in this way, 

 being- first raised to a cherry-red heat, and others only to the lowest 

 point necessary for liquefaction. The effects were the same in both : 

 no influence had been exerted over the hardness of the metal, and 

 the changes which usually occur are due to a little oxide introduced. 

 In experiments upon the influence of time it was found that, after 

 a minute had elapsed, the effect of time was masked by the general 

 effect of the metal, and nearly hidden. For a charge of 1950 kilo- 

 grammes the compressions were as follows : 



Time . . 30" 45" 60" 75" 90" 120" 

 Thickness 365 331 322 321 319 313 



So that here, after a minute, 10" produced an effect of only 2 de- 

 grees upon the scale. Still it was found the effect did proceed ; 

 for with a charge of 1760 kilogrammes the effect was as follows : 



Time ... 1 minute 1 hour 24 hours 

 Thickness 317 245 223 



So that, after 24 hours, the lead still continued to give way. 



The most important conclusion from these experiments is, that 

 lead fused and cast in the open air is of variable hardness, and that 

 to obtain it with its true and constant power of resistance, it must 

 be cast out of contact of air, and drawn off from the bottom of the 

 mass *. 



3. ON THE POWER OF HORSES. ( B. Bevan, Esq.) 



The following experimental data are from a letter written by Mr. 

 Bevan to the Editors of the Philosophical Magazine. 



" In the period from 1S03 to 1809 I had the opportunity of 

 ascertaining correctly the mean force exerted by good horses in 

 drawing a plough ; having had the superintendence of the experi- 

 ments on that head at the various ploughing matches both at Wo- 

 burn and Ashridge, under the patronage of the Duke of Bedford 

 and the Earl of Bridgewater. I find among my memoranda the 

 result of eight ploughing matches, at which there were seldom 

 fewer than seven teams as competitors for the various prizes, 



* Annales dc Chiinic, xliv. p, 103, 



