April 15, 1910] 



SCIENCE 



bll 



Mr. Milton C. Whitaker, M.S., general 

 superintendent of the Welsbach's Company's 

 works, has been appointed professor of indus- 

 trial chemistry, at Columbia University, to 

 the vacancy caused by the retirement of Pro- 

 fessor Charles F. Chandler. Dr. Marston 

 Taylor Bogert has been appointed to succeed 

 Dr. Chandler as head of the department of 

 chemistry. 



At Harvard University, Dr. H. W. Morse, 

 in physics, and Dr. L. J. Henderson, in bio- 

 logical chemistry, have been promoted to as- 

 sistant professorships. Dr. W. R. Brineker- 

 hoff has been appointed assistant professor of 

 pathology and Dr. S. B. Wolbach, assistant 

 professor of bacteriology. 



Walter T. Marvin, A.B. (Columbia), Ph.D. 

 (Bonn), preceptor in Princeton University 

 since 1905, has been appointed professor of 

 mental philosophy and logic in Rutgers Col- 

 lege. 



Dr. Arthur Willet, F.R.S., director of the 

 Natural History Museum at Colombo, Cey- 

 lon, and marine biologist to the Ceylon gov- 

 ernment, has been appointed professor of zo- 

 ology at McGill University. Dr. Willey, a 

 graduate of Cambridge, acted for some years 

 as tutor in biology in Columbia University. 



DISCUSSION AND CORRESPONDENCE 

 V air currents in mountain valleys 

 To the Editor op Science: Mr. Varney's 

 interesting account of the control of cliii 

 shadows on air currents observed in the val- 

 leys of the Canadian Selkirks, which appeared 

 in a recent issue of Science, prompts the fol- 

 lowing report of some facts of a similar na- 

 ture noted in the Tosemite Valley. 



The lay and configuration of the steep- 

 walled Yosemite trough are such that at no 

 hour of the day, even in mid-summer, are its 

 two sides fully sunlit throughout: there are 

 always clifE shadows here and there; while 

 some dwindle, others grow. The effect of this 

 alternation of light and shadow upon the air 

 movements along the valley sides is most 

 marked, indeed it fairly forces itself upon 

 one's attention when traveling on any of the 



zigzag trails that lead up out of the valley. 

 On a sunlit slope the dust from the horses' 

 feet floats slowly upward in a golden cloud 

 that accompanies the ascending traveler in a 

 truly exasperating manner. On a shaded 

 slope, the dust cloud pours at once over the 

 edge of the trail, so that parties descending 

 rapidly from zigzag to zigzag constantly meet 

 their own dust wafting down upon them from 

 above. Obviously, the logical thing to do, in 

 order to have a dust-free journey, is to time 

 one's ascent for an hour when the trail is in 

 shadow, and one's descent for an hour when 

 the trail is sunlit. This principle, after it was 

 once understood, was indeed deliberately put in 

 practise by the writer on all occasions when the 

 choice of hour mattered little otherwise — al- 

 ways with the desired result. Some trails, 

 like that to the Tosemite Falls, lie as a rule 

 partly in sun, partly in shadow, and on them 

 the trips were arranged so as to avoid the 

 dust on those stretches where experience had 

 shown it to be densest. 



In the Tosemite Valley, as in many other 

 mountain valleys, there is further a pro- 

 nounced general air movement lengthwise 

 through the trough, proceeding up valley in 

 the day time and down valley at night. The 

 rhythmic regularity with which it reverses in 

 the early morning and in the late afternoon, 

 was made strikingly manifest during the 

 summer of 1905, when severe forest fires near 

 the lower end of the valley sent up a gener- 

 ous volume of smoke in the otherwise pure at- 

 mosphere. Every morning the valley was 

 clear, having been swept out, so to speak, by 

 the nocturnal down-valley current, and the 

 pall could be seen floating oS to the south- 

 west, down the Sierra flank. But, as the 

 shadows in the valley trough began to shorten 

 and progressively larger areas became inso- 

 lated, a moment would soon come when the 

 warm up drafts gained the upper hand, and 

 the up-valley current would be inaugurated. 

 Then, the smoke would creep up the valley, 

 becoming denser by degrees, until by nine or 

 ten o'clock one could scarcely see across from 

 rim to rim. This condition would prevail all 

 day, until with the lengthening of the shadows 



