Volume 1

William Whewell, D.D., Master of Trinity College, Cambridge : an account of his writings with selections from his literary and scientific correspondence / by I. Todhunter.

  • Isaac Todhunter
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: William Whewell, D.D., Master of Trinity College, Cambridge : an account of his writings with selections from his literary and scientific correspondence / by I. Todhunter. Source: Wellcome Collection.

    429/456 (page 393)
    Ulloa on Iris journey to measure a degree of latitude in Peru saw a volcano on the moon’s surface during a total eclipse of the sun (Chladni, p. 415). [I do not know to what hook reference is here made; Ulloa s observation belongs, I think, to a much later date than his labours in Peru.] Herschel saw one, as he tells us m the Philosophical Transactions for 1787. Piazzi saw one in 180o. Schroter several times saw appearances in the moon which proved the fact. On the 28th of September, 1788, he saw on the border of the Mare Imbrium a luminous appearance, and soon afterwards, on the 12tli of October, he saw a new crater. And again between Jan. 7 and April 5, 1789, according to his observations, two new craters had appeared within a circuit of eight miles. These observations demand far more notice, I may say more credit, than they have obtained. Our discoverers found active volcanoes, though, as I have said, very intermittent m their action, and these they carefully studied. They found that some of these intermittent volcanoes have a considerable regularity in their action, and make their eruptions at fixed intervals, so that the eruption can be foreseen and reck- oned upon. In particular, near the center of the moon’s volcanic disk there is a smooth plain which your selenograpliers have called Sinus iEstuum, and rising from this plain is a ring-formed crater. This crater was found to make its eruptions at intervals, for some years at least, of once in five of our days (your months). These eruptions were observed with great care by oui philoso- phers ; the matters ejected were observed with instruments con- structed for the purpose, and followed by the eye as far as they could be seen. The velocity with which they were projected was so great that they went off into space and returned no more. You must recollect that there is no air to impede their motions, as there is in your terrestrial volcanoes: so that even small masses, cinders and ashes, thus projected, went away and returned no more to the surface of our planet. But moreover our observers discovered that along with smaller masses, there were ejected larger ones; also it seemed, in a certain order. Every seventh eruption a large mass was observed to proceed from the crater and to mount up into the zenith till it disappeared fiom their vision.