August 30, 1894] 



NA TURE 



431 



and it is shown that the amplitude of the variation at the 

 northern station is four times as great as at the southern. The 

 author also considers that the small variations whici canstitute 

 the 26-day period variation are not due to a direct mi?n;tic 

 action of the sun, but that they must have their origin in so.ne 

 secondary action of the same. 



In cases where it is desired to -investigate a ray of light 

 reflected perpendicularly from a surface, it is usual to employ a 

 transparent plate of glass which transmits the incident ray before 

 it falls upon the surface, and partially reflects it aside on its 

 return. Such an arrangement, best known in Gauss's eye-piece, 

 may be called a Gauss's plate. The best position of such a plate 

 is, as pointed out by Ilerr B. Walter in the current number 

 of Wiedemann s AnnaUn, not the commonly accepted one 

 of 45°, but another depending upon the refractive index of the 

 material of the plate, and upon whether the light is polarised 

 and in what manner. From theoretical considerations, he 

 concludes that for light polarised either in or at right angles to 

 the plane of incidence the greatest possible intensity of the 

 reflected light is 15 per cent, of the original intensity, whatever 

 may be the refractive index. If the light is polarised in the 

 plane of incidence, the plate must be placed at a lesser angle to 

 the ray the smaller the index of refraction. For light polarised 

 at right angles to this plane the reverse holds good. But for 

 refractive indices about i '4 this angle reaches the common value 

 of i' 46' 16'. The best position for ordinary light may be 

 determined by regarding it as composed of the two species of 

 polarised light. For crown glass the inclination should be loi°, 

 at which position the intensity of the reflected light is 2 '84 times 

 that obtained with the usual inclination of 45°. 



A NBW automatic sounding instrument has lately been 

 brought into use by Captain G. Rung, the director of the 

 Copenhagen Meteorological Institute, under the name of the 

 universal bathometer. Unlike the instruments hitherto con- 

 structed, which register the depth attained by the compression 

 undergone by a column of air. Captain Rung's bathometer, as 

 described in jWj«ja, measures the density of a sm ill volume of 

 the compressed air cut off at the bottom of the sea. This 

 density is directly propartional to the depth attained, ard is 

 measured by allowing the compressed air to expand until it 

 is under atmospheric pressure only. Its volume will then be 

 proportional to the density it had reached during compression. 

 The whole apparatus is very neat and compact. .\ metallic 

 tube contains two other tubes side by side, both communicating 

 with a small chamber at the top. A valve shuts off the com- 

 munication with the one or the other of the tubes, accordingly 

 as the sounder is being lowered or raised. When the bathometer 

 is being let down, water enters the " air tube " from the bottom, 

 and compresses the air in the tube a'nd in the small chamber. 

 The whole is enclosed in another heavy tube, in which it can 

 slide a little up and down. When the bathometer touches the 

 bottom, the inner tube slides down, thereby turning the valve so 

 as to close the communication with the air tube and open to the 

 "measuring tube." At the same time, a couple of spring 

 catches prevent the inner tube sliding up again. The 

 bathometer is then drawn up to the surface, and the reading 

 on the measuring tube at once indicates the depth. This tube 

 is made of glass, and is graduated in fathoms or other units of 

 length at equal intervals. This constitutes the chief advantage 

 of this over previous types. In instruments measuring the 

 depth by the volume of the compressed air the graduations had 

 to be at smaller and smaller intervals as the depth increased, 

 since the amount o! compression decreases at high pressures. 

 Captain Rung's instrument, on the other hand, can be graduated 

 directly up to any limit of depth which it is likely to attain. 

 NO. 1296, VOL. 50 



Mr. W. J. MOENKHAUS has lately studied a species of 

 American freshwater Percidce — Etheostoma caprodes, Rafinesque 

 — with a view to ascertain the extent of its variation, the relation 

 of its variation to its geographical distribution, the extent of 

 variation in each locality, and the variation with age. He gives 

 an account of his investigation in the American Naluraliit for 

 August, and from it we learn, among other paints, that the 

 difference between specimens from the same locality is very 

 slight. The greatest variation was found to be in the colour- 

 patterns of the fish, but the most complicated colour-pattern 

 can be connected with the simplest by means of intermediate 

 stages. These variations, however, could not be connected 

 with the latitudes inhabited by the different varieties. Slight 

 variations were found in proportions and number of fin rays. 



The Plankton Expedition has yielded some very interesting 

 results with regard to the bacteriology of the ocean, which are 

 now published by Dr. B. Fischer in " Die Bakterien des 

 Meeres nach den Untersuchungen der Plankton-Expedition." 

 Except at very great depths, germs capable of germination 

 were found everywhere. The number in the Canary, Florida , 

 and Labrador currents was larger than in the south equatorial, 

 north equatorial, and Guinea currents. None could be detected 

 with certainty in the bed of the ocean ; but bacteria abound at 

 a depth of 400m., and are certainly present at depths between 

 800 m. and I loom. The prevailing form of microbe is the 

 spiral ; but bacterium forms are also frequent ; micrococci are 

 rare. Forms more or less resembling the cholera-vibrio, both 

 in their form and in their mode of motion, were very common. 

 Most marine bacteria are aerobic, but some appear to be also 

 facultatively anaerobic. Not a few form pigments, and a large 

 number are luminous in the dark; the phosphorescent forms 

 were most commonly met with on the surface of living fish. A 

 number of new species are described. 



Some interesting points await settlement in the natural 

 history of the moUusk Gundlachia, whose shell presents such 

 puzzling and anomalous features. In a recently published paper 

 on the Australasian forms {Proc. Linn. Soc. if.S.lV. viii. 

 1893), Mr. Charles Hedley briefly reviews our knowledge of 

 the genus and its distribution, and gives descriptions and figures 

 of G. pctterdi and G. beddomci. In the case of the former 

 species, he describes a series of young shells showing the method 

 by which the primary Ancylus-WVe. shell is transformed into the 

 curious double shell of the adult. Stimpson's suggestion that 

 the septum which partially closes the aperture of the primary 

 shell should be compared physiologically with the epiphragm 

 of the Ilelices^as a protection during hibernation — well de- 

 serves some attempt at verification; as also does the unproved im- 

 pression that under particular conditions the shell of Gundlachia 

 never attains its normally double form, but remains simple and 

 patelliform throughout life. 



The July number of Modern Medicine and Bacteriological 

 Review contains an article entitled " The Value of Prof. Koch's 

 Discovery," in which it is mentioned that the State of New 

 York has recently passed a law authorising the use of tuber- 

 culin as a means of determining the presence or non-presence 

 of the tuberculous process in cows. It is poiaied out that 

 though Koch's tuberculin has not fulfilled th: expectations 

 raised for it as a curative agent, as a means of diagnosis it 

 may be of great service. Two or three drops of tuberculin 

 injected beneath the skin of a cow will, if the animal is tuber- 

 culous, give rise within a few hours to an elevation of tempera, 

 ture of several degrees, whilst this characteristic reaction is 

 absent in the case of animals free from this disease. Amongst 

 the bacteriological notes is one on soap as a germicide, from 

 which it appears that the so-called antiseptic soaps containing 



