334 PROCEEDINGS OF THE AMERICAN ACADEMY 



presently a little liquid lava would ooze forth, and the flow would 

 detach itself, sinking at its outer margin, or seeming to be hurried 

 obliquely downwards under the molten mass. In this manner floe after 

 floe was hurried out of sight, until the molten portion had all around 

 gained the bank. 



Professor N. S. Shaler spoke of tlie effect of changes in the 

 temperature of the moon's surface. Mr. Harrison has shown 

 that this amounts to about 960° F., or from — 100° to 840°, 

 assuming the specific heat equal to that of quartz. The effect 

 of such a change on a level plain like the Mare Humorum would 

 be to alter its length half a mile. He proposed to detect such 

 changes by accurate measurements of known points on the 

 moon's surface. So great a variation in temperature would 

 account for the observed alterations of color which have been 

 ascribed to a rapid growth of vegetation. 



Professor Benjamin Peirce suggested that these changes in 

 position could be best measured on Mr. Rutherford's photo- 

 graphs of the moon, points near the centre of the disk being 

 selected and measured during the first and last quarter. 



Professor E. C. Pickering expressed a doubt whether this 

 method would possess sufficient delicacy, as a variation of one 

 mile would equal only about a second of arc, and the measure- 

 ments would be complicated by libration, and all the consider- 

 ations which render so uncertain the moon's diameter. 



Professor Benjamin Peirce referred to the Coast Survey 

 steamer now preparing to go to the Pacific for scientific pur- 

 poses. With a capacity of 350 tons it can make 200 miles a 

 day, while burning less than three tons of coal. Therefore, it 

 can carry enough of the latter for a voyage of 8000 miles. 

 The statement of Dr. Lardner, that no steamer under 500 tons 

 could cross the Atlantic by steam alone, is thus completely dis- 

 proved, as this vessel could easily make the trip and return 

 without recoaling. 



