VOL. LI.J PHILOSOPHICAL TRANSACTIONS. ^gi 



ancient records from copies of them that were got abroad, and probably the stan- 

 dards at the same time. The congius was restored by weight, according to the 

 Plebiscitum Silianum, as the inscription on it testifies. The quadrantal was too 

 cumbersome a vessel for common use, to which the congius (like our gallon) 

 was well adapted i so that Mr. R. does not see what other purpose it could serve, 

 but to adjust the congius to its capacity, and the foot to its side : but here we 

 see the congius adjusted by weight, and it is not very likely that a new quadran- 

 tal should be made for no other end but to adjust the foot by, when so many 

 copies of the old standard were extant. Therefore it is not improbable that the 

 standard of the foot was at this time restored, without any regard to its relation 

 to the quadrantal. 



But as to the difference between the foot derived from the congius, and that 

 found from other authorities, Mr. R. further observes, that the correct adjust- 

 ment of weights to measures is a very difficult matter, even in this age and in this 

 kingdom, where workmanship is arrived at a high pitch of accuracy. And what 

 errors rude workmanship is liable to, sufficiently appears from the weights Paetui* 

 and Villalpandus have given of the congius. Therefore he sees no reason to 

 reject the testimonies of those authors, who say that the cubic foot contained a 

 quadrantal of wine; and as little to believe that these two standards were ever 

 truly adjusted to each other. 



But had the original standard of the Roman foot been truly adjusted to the 

 quadrantal, and continued invariable from the time of its first establishment, yet 

 a false measure of it might at one time or other have got into common use at 

 Rome, as well as a false measure of the French foot did at Paris ; where in the 

 year 1 668 the mason's foot was found to exceed the foot of the Chatelet by -^ 

 of a Paris inch, which is above ^ of a London inch : and the unaccountable 

 negligence which appears in the Roman coinage, gives sufficient ground to sus- 

 pect that they were not more accurate in their measures. 



LXX. Description of a Metalline Thermometer. By Keane Fitzgerald, Esq. 



F. R. S. p. 823. 



Mr. Boyle, the great promoter of experimental philosophy, made a thermo- 

 meter on the principle of air, which to a certain degree of heat or cold, answered 

 very minutely. Alcohol, or spirit of wine, has been more generally used ; but 

 has been found to lose in time much of its expanding quality; and also to be 

 frozen by an intense degree of cold. Mercury, as not deemed subject to these 

 inconveniencies, has therefore been allowed the most proper for the purpose. 



Mr. Fahrenheit has since improved the mercurial thermometer to a great 

 degree, and brought it to as much perfection as perhaps it will bear. He has 

 remarked, that wlien the barometer shows a greater degree of pressure of the 



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