ASTRONOMY. 21!) 



latter theory was received by the Academy, it seems to be inadmissible 

 when the dynamics of the present solar system and the doctrine of 

 probabilities are called into play. On the other hand, if in the place of 

 rhe "considerable globe like the earth" Ave substitute, with Dv. r>all, 

 the earth itself, with its past certainties of enormous volcanic energy, 

 then the theory may have some plausibility. 



PLANETS. 



YuLCAiv' (!) — Dr. Swift, of Eochester, has announced his intention 

 of going to Africa to observe the total eclipse of the sun on May 10. 

 188L*. His special object is to look for the two intramercurial planet* 

 wbich appeared in the field of his telescope at Denver during the eclipse 

 of 1879. 



The Eaimh, geodesy, etc. — In the volume of the Comptes Rendus for 

 1880 of the International Geodetic Association for the measures of de- 

 grees in Europe, there is a remarkable map which shows at one glance 

 the triangulation of Europe. To be fully appreciated, the original 

 work must be consulted. 



The origin of the English mile. — At a recent meeting of the French 

 Academy of Science, a paper on a question of ancient metrology and 

 the origin of the English mile was read by M. Faye. He inquires into 

 the cause of the error, long current, of supposing the mile equivalent 

 in length to a terrestrial arc of one minute. The mile has been prob- 

 ably deduced from Ptolemy's measure, and the error of one-sixth seems 

 to arise from the English geographers having supposed that Ptolemy 

 used tlie Greek foot, which Eratosthenes used 400 years before, whereas 

 he used the Phileterian foot, which is about 0.36™, the earlier one bein-g 

 0.27™. Eratosthenes counted 700 stadia to a degree; Ptolemy only 

 about 500. 



The evaluation of Ptolemy, M. Faye concludes, is merely a sort ot 

 conversion of the excellent measure of Eratosthenes into units of 

 another epoch and different length. It must have lost, thus, a little 

 of its first precision ; but, as presented by Ptolemy, the English geog- 

 raphers had good reason to take it as base of an evalution of the arc 

 of one degree, and to offer it to nautical men of their country. Only, 

 and here is the mistake, they believed that the great Greek astronomer 

 used the Greek foot. This is one hundredth and a half more than the 

 English foot. If the English geographers of the sixteenth century 

 forced this evalution but a little and carried it to five hundredths, they 

 would have found 030 English feet to the stadium, which they believed 

 to have 600 Greek feet, and these 030 feet, or these 210 yards, multi- 

 plied by 500, would have given them 105,000 yards for the degree, and 

 exactly 1,700 yards to the mile. Tire English mile then has probably 

 been deduced from the measure of Ptolemy; its error of one-sixth is 

 due simply to confounding the Greek foot with the Phileterian foot. 



Hence the mile of l.GOU meters long passed as equivalent in length 



