8 Dugald Clerk, The Work and Discoveries of Joule 



included) equal to raise a weight of 331,400 lbs. to the 

 height of one ft., when the revolving magnets were moving 

 at 8 ft. per second. Now the duty of the best Cornish 

 steam engine is about 1,500,000 lbs. raised to the height of 

 one ft. by the combustion of one pound of coal, which is 

 equal to five times the extreme duty that I was able to 

 obtain from the electro-magnetic engine by the consump- 

 tion of a pound of zinc. This consumption is so< unfavour- 

 able that I confess I almost despair of the success of electro- 

 magnetic attractions as an economical source of power, for 

 although my machine is by no means perfect I do not see 

 how the arrangement of its parts could be improved so as 

 to make the duty of one pound of zinc superior to the duty 

 of the best steam engines per pound of coal; and even if 

 this were attained, the expense of the zinc and exciting- 

 fluids of the battery is so great compared with the price of 

 coal as to prevent the ordinary electro-magnetic engine 

 being useful for any but very peculiar purposes." 



Joule had reached 22 years of age and he had definitely 

 failed in his original purpose, but his three years of con- 

 tinuous research work in his father's house had given him an 

 education in science which he could not have obtained at that 

 time in any other way. 



He continued his investigations on heat, but he did not 

 at once definitely connect heat and mechanical energy; his 

 paper of February 16th, 1841, linked chemical and mechanical 

 effect in definite ratio. He first connected heat with mechani- 

 cal energy in the beginning of 1843, and by August of the 

 same year he was able to state generally : — 



" The quantity of heat capable of increasing the 

 temperature of a pound of water one degree of Fahrenheit's 

 thermometer scale is equal to, and may be converted into, 

 a mechanical force capable of raising 838 lbs. to a perpen- 

 dicular height of one foot." 



As it stands this statement is incorrect ; it assumes that 

 heat can be converted into work in the same proportion as is 

 found when work is converted into heat. Joule had proved 

 the accuracy of the latter proposition, but thought that his 

 proof included the former also. 



Joule made further determinations by using a paddle rotated 

 in water and other liquids to obtain the heat evolved bv the 

 disappearance of mechanical energy, and as a final result of 



