June 17, 1921] 



SCIENCE 



557 



rotation of the plane of the wave front, which 

 would not increase the apparent diameter of a 

 star. 



In the case of either an orbital displacement 

 or a rotation of the wave front, the observed 

 deflection decreases with the distance ,and 

 would be inappreciable at stellar distances. It 

 can be shown that the sun at the distance of 

 the nearest star would show a displacement at 

 the limb, on the Einstein hypothesis, amount- 

 ing to less than one millionth of a second of 

 arc, if the deflected beam originated in a neigh- 

 boring companion. 



Keivin Burns 



Allegheny Obseevatoet 



russian scientific men 

 To THE Editor of Science: Attention has 

 been called in Science to the British " ap- 

 pointments committee for Eussian scientific 

 and literary men," imder the chairmanship of 

 Sir Arthur Schuster. Many Eussians dis- 

 tinguished in various branches of learning are 

 at present scattered over European countries, 

 some of whom are destitute, while others are 

 earning a precarious livelihood by work in 

 which they have no opportunity of exercising 

 their particular capabilities, the world at large 

 thus losing the benefit of their knowledge and 

 aptitude. 



The object of the committee is to bring the 

 names and qualifications of some of these 

 men to the notice of universities and other 

 institutions outside of Eussia which may be 

 able to offer them suitable employment. Lists 

 of these names have been sent by the com- 

 mittee to various universities and organiza- 

 tions and the National Eesearch Coimcil has 

 just arranged to send similar lists to the presi- 

 dents of about two hundred colleges and 

 universities in this country. 



The council has also received a circular let- 

 ter from a committee of meteorologists and 

 geophysicists of Vienna which asks if cer- 

 tain kinds of statistical and preparative work 

 needed by meteorologists and geophysicists of 

 this country can not be done, for pay, in 

 Vienna. These meteorologists and geophysi- 

 cists have access to many valuable sources of 



statistics and general data and appeal for op- 

 portunity to do this work in order to assist in 

 supporting themselves. Any communications 

 which it may be desired to make to this com- 

 mittee should be addressed to Dr. A. Wagner, 

 Zentralanstalt fiir Meteorologie, Hohe Warte 

 38, Vienna XIX. 



Vernon Kellogg 

 National Eesearch Council 

 May 27, 1921 



SPECIAL ARTICLES 



A CONVENIENT CULTURE MEDIUM FOR 



DAPHNIDS 



Daphnia and other Cladocera may be fed 

 upon certain unicellular green algse, a mix- 

 ture of various protozoa and protophyta ob- 

 tained from the sediment of ponds in which 

 there is a considerable quantity of organic 

 matter, or upon bacteria. 



For more than five years the writer suc- 

 cessfully utilized material from ponds in ob- 

 taining food for Cladocera cultures repre- 

 senting several species. The somewhat dis- 

 colored water was dipped up in such a man- 

 ner as to obtain considerable amounts of the 

 loose fluffy sediment lightly resting upon the 

 bottom. In the strainings which followed 

 (through silk bolting-cloth, to prevent con- 

 tamination of the laboratory stock) much of 

 this sediment was rubbed through the strain- 

 ing cloth and distributed with the water to 

 the culture bottles (about 100 c.c. in quantity 

 in ordinary wide mouthed 200 c.c. bottles). 

 This method of obtaining culture water con- 

 taining the proper food organisms has cer- 

 tain limitations. The water and sediment 

 from most ponds do not constitute a proper 

 culture medium; a pond from which a good 

 culture medium may be obtained is hard to 

 iind. Further from month to month and sea- 

 son to season such a pond undergoes wide 

 fluctuation in its usefulness as a source of 

 daphnid food; it may even dry up and one's 

 Cladocera material be imperilled or lost. 



Some workers using algse have cultivated 

 them in jars of water; others on agar plates. 

 The necessity for obtaining just the proper 

 sorts of algse and the requisite skill in their 



