Februakt 23, 1917] 



SCIENCE 



187 



The University of Stockliolin has received 

 from Mrs. Amanda Euben the sum of 50,000 

 kroner to found a readership in experimental 

 zoology. 



Dr. B. C. Ceowell, professor of pathology 

 and bacteriology, University of the Philip- 

 pines, has been appointed director of the Grad- 

 uate School of Tropical Medicine and Public 

 Health of that university. This school gives 

 courses which in one year lead to the degree of 

 Doctor of Tropical Medicine and in two years 

 to Doctor of Public Health. 



Dr. H. B. Fantham, of Christ's College, 

 Cambridge, has been appointed to the pro- 

 fessorship of zoology at the South African 

 School of Mines and Technology, Johannes- 

 burg, and Dr. C. E. Moss, of Emmanuel Col- 

 lege, has been appointed professor of botany in 

 the same institution. 



We learn from Nature that Dr. Johanna 

 Westerdijk has been appointed associate pro- 

 fessor of phytopathology in the University of 

 Utrecht. She is said to be the first woman to 

 receive such an appointment in Holland. 



DISCUSSION AND CORRESPONDENCE 



THE LIMIT OF THE SPECTRUM IN THE ULTRA- 

 VIOLET 



In the Astrophysical Journal for March, 

 1916, I gave an account of my work in the 

 extreme ultra-violet. During the past year I 

 have continued my investigations in the same 

 field; the results have not been commensurate 

 with the labor, but it is jjerhaps worth while to 

 make a brief report of them. 



I have not changed the general design of my 

 spectroscope but I have replaced the 100 cm. 

 grating by one of 50 cm. radius, thus halving 

 the light path and considerably reducing the 

 volume to be exhausted. My source of light is 

 stiU a quartz discharge tube, but I have so al- 

 tered the design that the end of the capillary 

 can be brought much nearer the slit of the 

 spectroscope than before; I have considerably 

 increased the potential of the transformer; as 

 before, I employ helium at one or two milli- 

 meters pressure to fill my spectroscope and 

 discharge tube. 



The net result of these changes is that I have 

 certainly extended the spectrum from 600 to 

 the neighborhood of 510 Angstroms; a trace 

 of a line exists on my very best negative near 

 450 Angstroms, but it is far too faint to afiord 

 trustworthy evidence. 



Prom time to time during the past five or 

 six years I have tried Wood's miniature arc in 

 vacuimi, and a variety of vacuum spark ar- 

 rangements, recently I have repeated the more 

 promising of these experiments. 'None of these 

 sources appear to yield lines in the most re- 

 frangible region. Helium continues the most 

 promising source. Theodore Lyman 



Jepperson Physical Laboeatort, 

 Harvard University, Cambridge, 

 February 14, 1917 



THE FOUNDATIONS OF DYNAMICS AND 



DADOURIAN'S ANALYTICAL 



MECHANICS 



My attention was called recently to a review 

 of the second edition of my " Analytical 

 Mechanics" by Professor E. W. Eettger, 

 which appeared in Science (No^ 1130) last 

 summer when I was in the mountains and did 

 not see it. The review on the whole was 

 favorable and would not have tempted the 

 author of the book to make an answer at this 

 late date were it not for the fact that the two 

 questions raised by the reviewer bear upon the 

 foundations of the science of mechanics. 



The first of these is directed against my 

 direct application of the laws of vectors to the 

 directed magnitudes of mechanics: 



Before we apply the law of vector addition to 

 any kind of quantity, ought we not first assure 

 ourselves that the parallelogram law holds for 

 these quantities? Since force, for instance, ia a 

 directed quantity (italics are mine) does it follow 

 that the parallelogram law holds for forces? 



I would answer both of these questions in 

 the afiirmative. We have no right to apply 

 vector operations to " any kind " of quantity. 

 We ought to assure ourselves that the quan- 

 tity in question is a " directed quantity " be- 

 fore treating it as such. But having once 

 assured ourselves of this fact we need not 

 hesitate to apply to it the parallelogram law 

 or any other law of directed quantities. 



