434 



SCIENCE. 



[N. S. Vol. III. No. 



des etoiles doubles, p. q.), that the application of 

 graphical methods to the problem in question 

 ought to cease with the drawing of the appar- 

 ent ellipse. After this has once been drawn, 

 the computation by Kowalski's elegant formulae 

 does not require more than half an hour. 



The same journal contains an account of some 

 very interesting experiments which have been 

 made at the Munich Observatory, by Dr. 

 Schwartzschild. A new form of micrometer has 

 been constructed, using the principle first em- 

 ployed in 1891 by Michelson for the measure- 

 ment of the satellites of Jupiter. This new 

 micrometer has been applied with the help 

 of a ten-inch telescope to the measurement 

 of a number of close double stars. Briefly 

 stated, the new instrument consists of a mov- 

 able plate, pierced with several slits, and 

 mounted outside the object glass of the tele- 

 scope. This produces a series of spectra of 

 both the principal star and the companion in 

 the field of view of the telescope. By revolv- 

 ing the slit plate until the spectra of both stars 

 are all in a straight line in the field of view, it 

 is possible to measure the position angle. Simi- 

 larly, by a sliding motion of the slit plate, the 

 spectrum of the companion can be made to ap- 

 pear exactly midway between two neighboring 

 spectra of the principal star. From a reading 

 of the scale attached to the slit plate it is then 

 possible to compute the angular distance of the 

 component from the principal star. The whole 

 apparatus is very simple and inexpensive, and 

 could be applied easily to any equatorial pro- 

 vided with a position micrometer. Thirteen 

 stars have been measured with this instrument 

 by two observers. The distance for the closest 

 double is 0".86, while the greatest distance 

 measured was 4". 25. Distances over five seconds 

 could not be measured accurately, because at 

 this distance the spectra begin to show too much 

 color for accurate observation. The probable 

 errors of these observations compare very fa- 

 vorably, indeed, with those obtained for other 

 forms of micrometric apparatus, especially in 

 the case of very small distances. But as is well 

 known, the very close doubles are the ones 

 most important to measure. 



The last number of the Astrophysical Journal 



contains an account of the progress made with 

 the new observatory of the University of Chi- 

 cago. An interesting feature of the new insti- 

 tution is to be a complete optical and mechan- 

 ical instrument maker's outiit. And an optician 

 as well as an instrument maker are to be per- 

 manently attached to the observatory staff. 



H. J. 



MARINE ORGANISMS. 



The Friday evening discourse at the Royal 

 Institution on February 29th was delivered 

 by Dr. John Murray, of the Challenger ex- 

 pedition, who spoke on 'Marine Organisms 

 and their Conditions of Environment.' Ac- 

 cording to the report in the London Times 

 Dr. Murray pointed out that in the distribu- 

 tion of marine organisms temperature was 

 a more important factor than in the case of 

 air-breathing and warm-blooded animals on 

 the land surfaces, although in the ocean the 

 extreme range of temperature never exceeded 

 52 deg. Fahr. In the surface waters of the 

 ocean there were five well-marked temperature 

 areas — an Arctic and an Antarctic cireumpolar 

 belt with a small range and a low temperature, 

 a circumtropical belt with a small range but a 

 high temperature, and two intermediate areas 

 with large annual ranges of temperature. The 

 waters of the ocean might be divided into two 

 great regions — the superficial region down to 

 about 100 fathoms, and the deep-sea region. In 

 the former, and especially in the marginal zone 

 surrounding the land, there was great variety 

 of conditions and an abundant fauna and flora, 

 whereas under the uniform conditions found in 

 the deep-sea plant life was absent, though there 

 was animal life in abundance. In the warm 

 surface waters of the tropics there were many 

 species, but relatively few individuals, while 

 the reverse condition was found in polar areas. 

 Again, in tropical pelagic regions organisms 

 secreting carbonate of lime were abundant, but 

 gradually disappeared towards the poles. In 

 the warm waters the pelagic larvse of bottom- 

 living species were always found, but in the 

 cold appeared to be absent. The lecturer was 

 of opinion that the various facts in the distribu- 

 tion of marine organisms might be accounted 

 for by supposing that in early geological times 



