SECT, i.] THE STEAM ENGINE. 39 



steam engine. His analytical knowledge was ample for the purpose, and the 

 access of the friend of Watt to practical data must have been easy in proportion as 

 Watt was the liberal friend of science ; therefore, much is expected when we take 

 up the volume which contains the articles of Dr. Robison on the steam engine. 



The first article contains a rather diffuse statement of the physical properties of 

 steam. The phenomena of boiling, and the effect of pressure in altering the 

 temperature necessary for ebullition, and the popular doctrines of latent heat, are 

 fully stated. It also contains a series of experiments on the elastic force of the 

 steam of water, and of alcohol (see art. 95 and 104) ; and we have only here 

 to remark on them, that they were not made with sufficient accuracy, even to 

 establish the justness of some of his own views on the subject ; also, the rule for 

 the elastic force of steam derived from these experiments, and stated to be " suffi- 

 ciently exact for practical purposes," is very far from being so, and has had a little 

 effect in misleading some of the engineers who have ventured to speculate on the 

 improvement of steam engines. But, on the whole, Dr. Robison's is the best 

 article on steam I have seen. 



The article on the steam engine consists of the history, mixed with detailed 

 descriptions, of the engines of Savery, Newcomen, Watt, &c. ; and such theoretical 

 discussion as he has given is also blended in the same mass. In the historical 

 portion the memory of Papin is not quite so respectfully treated as we could have 

 wished ; and the circumstance of Watt being the private friend and countryman 

 of the author has not been without its effect on the historian. In other respects 

 Dr. Robison has been impartial. In description there is a want of system, but 

 he is full and particular ; and he has been of unknown value in giving informa- 

 tion to the competitors of Boulton and Watt, and in furnishing matter for minor 

 writers. In theory he has reprinted the speculations of Bossut respecting the 

 best velocity for atmospheric engines, with some additions, and Watt's mode of 

 computing the pressure on the piston of the expansive engine ; but neither 

 of these inquiries are conducted in such a manner as to be of use to engine 

 makers. 



The reputation of Dr. Robison has given much additional value to his articles 

 on the steam engine : hence their effect has been unparalleled ; and if we find 

 little of novelty in his labours, it was no small favour to have the scattered know- 

 ledge on the subject collected with so much skill, and treated with so much clear- 

 ness and good taste. 



51. A modification of Watt's manner of constructing boiler fire places was 

 contrived in 1800 by Messrs. Roberton, of Glasgow, which is more convenient in 

 practice, though the same in principle. (See Sect, m.) They also attempted to 

 make the steam which escapes by the sides of pistons useful in adding to the 



