468 



NATURE 



[September i6, 1897 



gives a valuable summary of the explorations and surveys 

 made in 1895, and the museum and other work earned 

 on under his direction. The separate reports contained 

 in the volume are as follows : — 



" The Country between Athabasca Lake and Churchill 

 River," by J. Burr Tyrrell and D. B. Dowling. 



"The Geology of a Portion of the Laurentian Area 

 lying to the North of the Island of Montreal," by Frank 

 D. Adams. 



" Explorations in the Labrador Peninsula, along the 

 East Main, Koksoak, Hamilton, Manicuagan, and portions 

 of other Rivers, in 1892-93-94-95." by A. P. Low. 



" Report of the Section of Chemistry and Mineralogy," 

 by G. C. Hoffman. 



" Report of the Section of Mineral Statistics and 

 Mines," by E. D. Ingall. 



These reports are published separately, and several of 

 them have already been referred to in our columns of 

 " Notes." 



A Bibliography of Science. By William Swan Sonnen- 

 schein. (London : Swan Sonnenschein and Co., Ltd., 

 1897.) 

 This classified list of scientific books, extracted from two 

 useful bibliographies prepared by the author a few years 

 ago, will be valuable to readers who are outside the j 

 living stream of scientific thought. It is in no sense j 

 complete, and it does not pretend to be so ; nevertheless, 

 it will serve a useful purpose. Some of the remarks 

 of the editor may be resented by the authors of the j 

 books referred to. Thus, one book is described as "a | 

 somewhat slovenly and unscientific performance" (p. 

 384). If the criticism is a just one, the title of the 

 book might have been omitted. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself 7-esponsible for opinions ex- 

 pressed by his correspondents. Neither can he tindertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.^ 



Zeeman's Phenomenon. 



In Section A at the Toronto meeting of the British Associa- 

 tion, Dr. Ledge raised the question as to whether we should 

 expect on a simple theory that the spectral lines should be simply 

 widened or be doubled by magnetic force. The simple theory 

 depends on the acceleration or retardation of electrons perform- 

 ing circular orbits under the action of a magnetic force normal 

 to the plane of the orbit. If the plane of the orbit be not 

 normal to the magnetic force, it might appear that the accelera- 

 tion or retardation would be only that due to the component of 

 the force normal to the plane of ihe orbit. From this it would 

 follow that the lines would be widened and not doubled, because 

 every intermediate acceleration or retardation would occur 

 between the extreme cases of orbits perpendicular to the 

 magnetic force. This suggested theory, however, overlooks the 

 effect of the magnetic force in altering plane of the orbit. The 

 complete theory can be very much more simply obtained by 

 another method of attack. The motions being assumed simply 

 periodic in the undisturbed motion, can be resolved for each 

 electron into three linear vibrations, two at right angles to the 

 magnetic force and one parallel to it. This latter is undisturbed 

 and gives no light in the direction of the magnetic force. Each 

 of the other linear vibrations is disturbed, and we can easily see 

 how by considering that a linear vibration may be considered as 

 due to two circularly polarised vibrations. Each of these com- 

 ponent circular vibrations will be altered by the magnetic force 

 normal to its plane, one being simply accelerated and the other 

 retarded. We can consequently see that this more complete 

 theory leads to the conclusion that the lines would be doubled 

 and not widened, though, of course, they may be also widened 

 owing to other disturbances of the motion. There would be no 

 difificulty in writing down the equations of the resulting motion 



of the electron, but it seems hardly necessary to do so, as this 

 geometrical analysis leads to the kind of vibration emitted, which 

 is all that we can observe. Geo. Fras. Fitzgerald. 



Fort William, Ontario, August 28. 



Coccoliths in our Coastal Waters. 



Although much has been written about the problematical 

 coccoliths, the presence of these bodies in our coastal waters 

 does not appear to have been recorded. Our observations on 

 the minute marine organisms off this coast (South County Dublin) 

 show that they abound both near the shore and outwards to the 

 limits we have hitherto investigated — some three miles into the 

 Irish Channel. 



The following preliminary account of their mode of occur- 

 rence, and some features of their structure may be of interest. 



Our first finds were effected by means of a cone-shaped, 

 metal, surface dredge ; the wide end guarded with wire gauze — 

 about fifty meshes to the linear inch — and the narrow truncated 

 end closed with fine brass gauze, having about 350 meshes to the 

 linear inch. The dredge is floated horizontally by pine-wood 

 wings, and when in operation is trailed behind a boat, the wide 

 end forwards. At intervals the dredge is lifted, the finer gauze 

 removed and washed in a little sea water. 



Examination of the fine partiples so gathered reveals many 

 varieties of foraminifera, diatoms, a great abundance of peri- 

 dineos, sponge spicules, &c., and an amoeboid body resembling 





Difflugia, sp. (?), bearing a Coccolith X 900 diams. 



Difllugia pyriformis in appearance. This last body, magnified 

 about 900 diameters, is shown in Fig. i. The drawing shows 

 the organism as freshly dredged and extending finger-shaped 

 pseudopodia from the open collar, which terminates one ex- 

 tremity of its urn-shaped case. Most usually it is observed with 

 the pseudopodia retracted. 



The case enclosing the protoplasm is composed of minute 

 grains of quartz sand (resist acids and alkalies), adhering in 

 random fashion to the protoplasmic contents within. Also there 

 will be seen in the figure (which is from a camera-lucida draw- 

 ing) one small oval body, occurring among the sand grains. 



NO. 1455, VOL. 56] 



