22 



SCIENCE 



[N. S. Vol. XLII. No. 1070 



compared with three in 1838, about twenty 

 in 1880, about sixty in 1900, and now per- 

 haps two hundred. 



The stars the distances of which have 

 been measured have generally been specially 

 selected on account of their brightness or 

 large proper-motion. Each star has been 

 examined individually. Kapteyn has sug- 

 gested that instead of examining stars 

 singly in this way, photography gives an 

 opportunity of examining all the stars in 

 a small area of the sky simultaneously, and 

 picking out the near ones. The method has 

 been tried by Kapteyn and others — among 

 them Dr. Rambaut. The idea is very at- 

 tractive, because it examines the average 

 star and not the bright star or star of larger 

 proper-motion. It is liable, however, to 

 some errors of systematic character, espe- 

 cially as regards stars of different magni- 

 tudes. Comparison of the results so ob- 

 tained with those found otherwise will 

 demonstrate whether these errors can be 

 kept suiSciently small by great care in 

 taking the photographs. Until this is done 

 no opinion can be expressed on the success 

 of this experiment, which is worth careful 

 trial. 



The question may be asked. How near 

 must a star be to us for its distance to be 

 measurable ? I think we may say ten mill- 

 ion times the sun's distance. This corre- 

 sponds to the small angle 0.02" for the 

 parallax. If a star's parallax amounts to 

 this, there are, I believe, several observa- 

 tories where it could be detected with rea- 

 sonable security, though we shall know 

 more certainly by the comparison of the re- 

 sults of different observations when they 

 accumulate. 



You will readily imagine that an accu- 

 rate knowledge of the distances of many 

 stars will be of great service to astronomy. 

 There are ample data to determine the posi- 

 tions, velocities, luminosities and masses of 



many stars if only the distances can be 

 found. Thus we know the distance of 

 Sirius, and we are able to say that it is 

 travelling in a certain direction with a 

 velocity of so many miles per second ; that 

 it gives out forty-eight times as much light 

 as the sun, but is only two and a half times 

 as massive. The collection and classifica- 

 tion of particulars of this kind is certain to 

 give many interesting and perhaps surpris- 

 ing results. But it is not my purpose to 

 deal with this to-night. The task I set be- 

 fore myself in this lecture was to give an 

 idea of the difficulties which astronomers 

 have gradually surmounted, and the extent 

 to which they have succeeded in measuring 

 the distances of the stars. 



F. W. Dyson 



SCIENTIFIC NOTES AND NEWS 

 Fifty years ago William North Rice was 

 graduated from Wesleyan University, and two 

 years later was elected professor of geology and 

 natural histoi-y, a title which was changed to 

 professor of geology in 1884, when the depart- 

 ment of biology was established. Professor 

 Rice's services as teacher, administrator and 

 investigator were acknowledged by the confer- 

 ring on him of the degree of doctor of laws by 

 Wesleyan University at its recent commence- 

 ment. 



Dr. Victor C. Vaughan, professor of hy- 

 giene at the University of Michigan and presi- 

 dent of the American Medical Association, re- 

 ceived the honorary degree of LL.D. at the 

 annual commencement of Jefferson Medical 

 College, Philadelphia, on June 5. 



Three doctorates of science were conferred 

 by the University of Pennsylvania at its com- 

 mencement exercises on June 16. The recip- 

 ients and Provost Smith's remarks were as 

 follows: Robert Andrews Millihan — ^Physicist 

 of eminence, editor, whose investigations in 

 electricity, in molecular physics and heat have 

 won for you deserved and well-merited recog- 

 nition. Harry Frederick Keller — Because of 

 your profound knowledge of chemical science. 



