October 23, 1908] 



SCIENCE 



565 



thousand years ago extended, in certain direc- 

 tions, well into the temperate zones, seem to 

 offer positive evidence that the earth is grovp- 

 ing colder. The theoretical (heautifully 

 simple) explanation of the origin, groveth and 

 final retreat of the ice, which results from my 

 modification of Manson's hypothesis, is, very 

 briefly stated, as follows: 



After the minimum polar-surface-tempera- 

 ture had fallen to 0° C. snow commenced to 

 fall at the two poles during the respective 

 winter months ; each year this snow was, for 

 some time, completely melted during the re- 

 spective warmer seasons of the year; as the 

 earth grew colder, the snow and ice covering 

 became permanent and spread equatorwards 

 with seasonal fluctuations at the ice front; 

 but as the ocean grew colder the amount of 

 evaporation from its surface decreased, so that 

 the available amount of snow to be melted at 

 the ice front continually diminished (while 

 the intensity of the direct solar rays at the 

 surface of the earth was, for a given latitude,' 

 continually on the increase) f a final retreat 

 of the ice front was, therefore, inevitable. As 

 the snowfall will later on cease altogether, the 

 land ice will eontinxie to retreat and probably 

 disappear at the poles. These results are for 

 ideal sea-level conditions; topographic irregu- 

 larities, differences of elevation, direction of 

 air and water currents — all act to produce 

 great deviations from the theoretical results 

 here made to depend on latitude and ocean 

 temperature alone; these deviations have, in 

 the past, been so great that evidences of former 

 local glaciation should be found throughout 

 nearly the whole series of stratified rocks. 



In addition to the theoretical data given on 

 page 415 of the current volume of Science, I 

 would, in connection with Dr. Barrell's re- 

 marks on radiation of heat, call special atten- 



" Because of this condition of things, it seems 

 extremely probable that formerly, when the arctic 

 climates were less severe, equatorial and temperate 

 regions were for a time actually somewhat colder 

 than they are to-day, for the lowering of the 

 surface temperature resulting from the ever de- 

 creasing heat-trapping power of the atmosphere 

 was, for a time, probably more than offset by the 

 increased intensity of the direct solar rays. 



tion to the fact that, since the publication of 

 my paper demonstrating that Newton's law of 

 radiation is theoretically exact, no less au- 

 thority than Professor Newcomb has asserted 

 (but not demonstrated) that Stefan's law of 

 radiation has been established; now, as I 

 claim to have demonstrated that " some sur- 

 prising error in previous methods " has 

 actually developed. Dr. Barrell or some other 

 scientist must show that my demonstrations 

 are erroneous before further intelligent use 

 can be made of laws of radiation established 

 by others and used (to quote from Science, 

 February 14, 1908, p. 269) as "the formula 

 accepted to-day" by scientists. 



j. m. schaeberle 

 Ann Akbob, Mich., 

 September 29, 1908 



CLOUDS OVER A FIRE 



To THE Editor op Science: In connection 

 with Mr. B. M. Varney's letter on " Clouds 

 over a Fire" in Science for May 15, 1908, I 

 may say that I have often observed the same 

 phenomenon here. In cutting sugar cane 

 the stalks are stripped of leaves in the field, 

 and when the cutting of a field is finished the 

 leaves are set afire as they lie spread over the 

 field. When the weather is calm there arises 

 a column of dark smoke which is often beau- 

 tifully capped by a mass of white cloud. I 

 have wondered whether the particles of smoke 

 furnish nuclei for the formation of water 

 drops as the smoke rises to a level of super- 

 saturated air, or whether, as Mr. Vamey sug- 

 gests, the draft carries water vapor to a level 

 of cloud formation. 



Wm. F. Wallis 



EwA, Hawaii 



QUOTATIONS 



DANIEL COIT GILMAN 



Dr. Gilman was soon called from Cali- 

 fornia to conduct what was, at its inception, 

 a unique undertaking. This was nothing less 

 than the establishment of a university for 

 graduate study, with an equipment and 

 faculty that should make it the rival of the 

 best universities of Europe. On the disap- 



