January 23, 19 13] 



NATURE 



579 



by far the greater number of pearls are formed around 

 particles that are closely related to certain kinds of 

 shell substance. We might, in fact, divide the causes 

 of pearls into internal and external causes. The 

 external causes include worm and other parasites and 

 sand grains, and both are actually proved causes. 

 The internal causes appear to be more interesting, 

 and, so far as the pearls in the fresh-water mussel 

 {Margaritana tnargaritifera) and possibly the Ceylon 

 pearl oyster (Margaritifera vulgaris) are concerned, 

 seem to be the more important. The paper is well 

 illustrated, and as a short summary is admirable, 

 though many sections undoubtedly require more 

 detailed treatment. 



Dr. W. C. Sturgis has forwarded a copy of his 

 recently published "Guide to the Botanical Literature 

 of the Myxomycetes." This bibliography of an exten- 

 sive and important group of Protista, which has been 

 claimed alike by the botanist and the zoologist, gives 

 the titles of a very large number of publications 

 between the years 1S75 and 1912, and though the 

 compiler has confined his attention somewhat closely 

 to citations from botanical writers, thus omitting a 

 certain amount of valuable material in the fields of 

 cytology and physiology especially, it will prove ex- 

 tremely useful to students of these organisms, whether 

 botanical or zoological. The guide is issued by the 

 Colorado College, as Science Publication, vol. xii., 

 No. II. 



The annual report of the Director of Agriculture 

 for the Federated Malay States deals mainly with 

 rubber, and shows an astonishing development of this 

 crop. No fewer than 107,200 acres of land were 

 opened during the year, while the total output of 

 rubber was but little short of twenty-two million 

 pounds, against twelve and a half million of the 

 previous year ; prices were also well maintained. 

 Insect pests occur, but not to a serious extent ; accord- 

 ing to the entomologist, white ants {Termes gestroi) 

 are decreasing, and the other pests can now be con- 

 trolled. Fungoid diseases cause some trouble, 

 especially that brought about by Fames semitostus, 

 but this is now amenable to treatment. 



The Meteorological Committee has recently issued 

 the seventh edition of " A Barometer Manual for the 

 Use of Seamen." The work was originally issued by 

 the Meteorological Council in 1884, as a revise of the 

 " Barometer Manual " prepared by Admiral FitzRoy, 

 which had then been long out of print. Both these 

 manuals attained great popularity ; altogether about 

 25,000 copies of the revised editions were disposed of, 

 this large supply being partly due to the adoption of 

 the work as a text-book for mercantile marine ex- 

 aminations. The manual now under report (83 pp., 

 large 8vo) was prepared in the marine division of the 

 Meteorological Office under the superintendence of 

 Commander Campbell Hepworth, C.B. (marine super- 

 intendent). It differs from the last edition mainly by 

 the addition of certain paragraphs in the text, tem- 

 perature conversion tables, and other minor details, 

 and, like some of its predecessors (which have been 

 referred to in our columns), is well illustrated by 

 NO. 2256, VOL. 90] 



figures and by plates compiled from material in the 

 possession of the office. The sections dealing with 

 barometric pressure and its variations, with gales of 

 the temperate zones, and tropical storms are very 

 interesting and instructive, both for seamen and 

 others, and, as stated in the title, the work is really 

 "a text-book of marine meteorology." 



In the Proceedings of the Tokyo Mathematico- 

 Physical Society, vi., 17, Mr. T. Terada considers the 

 experimental fact that the velocities of earthquake 

 waves fall short of the values calculated by hydro- 

 dynamical methods. His analytical work is devoted 

 to examining whether this discrepancy can be 

 accounted for by the yielding of the earth's crust, 

 regarding the latter as a flexible bed resting on an 

 inner fluid magma. The results show that the ex- 

 planation is a plausible one, though the analysis in- 

 volves a number of assumptions not realised in 

 practice. 



For some time past, the belief that Newton's law of 

 gravitation is only approximate, and that the influ- 

 ence of a gravitative field depends on the time during 

 which it has existed, has received increasing attention 

 from physicists and astronomers. In a paper con- 

 tributed to the Wiener Sitzungsherichte (cxxi., i) 

 Prof. G. Jaumann builds up a theory of gravitation 

 based on a modification of Laplace's and Poisson's 

 differential equations. This modification consists in 

 the addition of an extra term proportional to the 

 time-flux of the potential, and it leads to the result 

 that in empty space the potential is propagated 

 according to the same law as temperature in the 

 diffusion of heat. The theory is applied to planetary 

 motion, variation of latitude, and conditions of 

 stability of the solar system. 



We have had an opportunity of e.xperimenting with 

 the "Rainbow Cup," which Mr. C. V. Boys showed 

 a few months ago at the Royal Society soiree, and 

 find it an interesting piece of apparatus. The cup 

 has its lip horizontal, and can be spun about a vertical 

 axis. When a soap film is placed on the top of the 

 cup and the cup then spun, the film thins rapidly in 

 the middle, and in a good light the display of colours 

 is brilliant. By altering the direction of rotation 

 coloured patterns can be produced which might be 

 used as the basis of decorative designs. By continu- 

 ing the rotation or by tilting the film a black spot 

 can be obtained and a study of its motions under 

 different conditions soon shows that it is thinner than 

 any other part of the film. The makers of the "Rain- 

 bow Cup" are Messrs. J. J. Griffin and Sons, Ltd., 

 Kingsway, W.C. 



We have received a copy of the second annual 

 report of the work of the Radiological Institute 

 attached to the University of Heidelberg, a report 

 which appeared in part 43 of the Elektrotechnische 

 Zeitschrift for 19 12. The institute was founded in 

 1910, has Prof. Lenard for director, and a further 

 staff of three assistant lecturers and demonstrators 

 in addition to an instrument-maker and attendant. 

 In the two years it has been in operation it has pro- 



