VOL. LIU.] PHILOSOPHICAL TRANSACTIONS. 70^ 



applied to a burse or exchange. The public roads are termed basilicae : and the 

 Christian writers took this word for their churches. Though this be the com- 

 mon use ot the word, it is not the primary. It signifies originally and principally 

 as it does in this inscription, a portico or colonnade, which being very large and 

 considerable in places built for courts of justice, for public auditories and meet- 

 ings of merchants, it came to pass that the name of the principal was sunk in 

 the adjunct; and all these places called alike basiiicae, from the colonnade, which 

 attended, and perhaps sometimes encompassed them, 



XXIX. A Method of Lessening the Quantity of Friction in Engines. By Keane 



Fitzgerald, Esq., F. R. S. p. ISQ. 



Mechanics, or that branch of mathematics which considers motions and moving 

 powers, their nature and laws, is properly distinguished into rational and practical. 

 Aknowledge in rational mechanics, which comprehends the whole theory of motion, 

 on which natural philosophy so greatly depends, is chiefly confined to the learned; 

 and the proper construction of engines and machines, which is the principal object 

 of practical mechanics, though so very necessary to carry on the several branches 

 of husbandry, manufacture, and commerce, on which the riches and power of a 

 nation in a great measure depend, is seldom attended to, but by the mere han- 

 dicraftsman ; who is little acquainted with the principles he works on, and from 

 whom no great improvements can well be expected ; yet it has sometimes hap- 

 pened, that excellent contrivances have been invented, for raising heavy weights, 

 and ovei'coming their resistances, by persons who never took the trouble of exa- 

 mining into the cause of gravity. It often happens that mechanical powers, 

 seemingly demonstrable in theory, are found very deficient in operation, from 

 unexpected obstructions ; which, with the expence and trouble that generally 

 attend the reducing speculations of this nature into practice, have probably been 

 the greatest obstacles to improvements in it. One of the greatest obstructions to 

 the mechanical powers of engines proceeds from the friction, or resistance of the 

 parts rubbing on each other ; which in general is greater or less, as the rubbing 

 parts bear the greater or less pressure ; and yet this obstruction is but little at- 

 tended to. The theorist makes no allowance on account of friction ; and the 

 practical mechanician, who feels the effects, yet, as if unavoidable, seldom takes 

 the trouble of searching for a remedy. Among the few who have endeavoured 

 to ascertain the quantity of friction proceeding from weight, some have deemed it 

 equal to -i-, others to 4^, and others more or less, according to their different 

 methods, or accuracy in making experiments. Doctor Desaguliers gives an ac- 

 count of some experiments, which show the quantity of friction in a cylinder, to 

 be equal to -§- of the power required to move it, when the surface of the cylinder 

 moves as fast as the power. 



