450 



SCIENCE. 



[Vol. I., No. 16. 



aquatic and amphibious mammalia (otters, 

 seals, whales, etc.), and others detrimental to 

 fish. As if this were not sufflcientlj- catholic, 

 division 40 is a trap to catch any interests not 

 already retained. It is defined as follows, un- 

 der the head ' scientific investigation : ' physi- 

 co-chemical investigation into those qualities 

 of salt and fresh water which affect aquatic 

 animals ; investigation of the bottom of the sea 

 and of lakes, shown b}' samples ; aquatic plants 

 in relation to fishing, etc. ; researches into the 

 aquatic fauna (animals of the several classes 

 preserved in alcohol, or prepared, etc.) ; appa- 

 ratus and implements used in such researches. 



Ten of the twentj'-three subjects announced 

 for the essaj's are purel3- biological, and many 

 of the others can be handled onlj- by scientific 

 investigators. 



The fisheries exhibitions of to-day are there- 

 fore more than their names would seem to 

 indicate. Perhaps thej- might more appropri- 

 ately' be called h3'drological exhibitions. Their 

 scope has increased as they have become more 

 popular. The first, held at Amsterdam in 1861, 

 was much less ambitious. Others followed at 

 Bergen, Norway (1865), Arcachon, France 

 (1866), Bologne (1866), The Hague (1867), 

 Aarhuus, Denmark (1867), Vienna (1867), 

 Gothenburg, Sweden (1867), Havre (1868), 

 Naples (1871), Berlin, London (1878); and 

 in Berlin, in 1880, the climax was apparentlj' 

 reached in a displaj', which, for extent and 

 completeness, no one supposed would ever be 

 surpassed. Great Britain h'as since had exhi- 

 bitions at Edinburgh, Norwich, and Tyne- 

 mouth ; and attention of the whole nation is 

 now concentrated upon the exhibition which 

 is to be opened by the Queen on the 12th. It 

 is generally admitted that it is the most impor- 

 tant exhibition held here since the Great ex- 

 hibition of 1851. Twentj'-five nations and 

 colonies are represented. In the catalogues 

 and in the announcements the place of honor 

 is given to the United States ; and the officers 

 do not hesitate to admit that the success of 

 the affair was largely assured by the pi-ompt 

 and liberal action of our government, — action 

 which may be regarded as, in part, an ac- 

 knowledgment of the very generous manner 

 in which England participated in our own ex- 

 hibition in Philadelphia in 1876. 



South Kensington, May 1. G. BrOWN GoODE. 



THE WEDGE-PHOTOMETER. 



This instrument has been attracting con- 

 siderable attention during the last year, and 

 has been especiallj- studied b^' Professor Pritch- 



ard of Oxford and Professor Pickering of 

 Harvard, to each of whom we owe a form of 

 the instrument. It depends for its efflcienc}' 

 on the accurate observation of the time of 

 extinction of the light of a star ; and as it is 

 evident that the various sources of error in 

 photometric work — moonlight, the state of 

 the atmosphere, the condition of the ej-es 

 of the observer, the position of observation, 

 whether that of comfort or constraint — would 

 affect a faint point of light near extinguish- 

 ment more than they would the brighter lights 

 used in other photometric methods, any con- 

 tribution to the question of the accuracy to 

 be expected from the wedge-photometer may 

 be of interest. 



The instrument employed by me is of the 

 form suggested by Professor Pickering. It 

 was made b^' Mr. J. Grunow of New York, 

 and seems to be very good work. It consists 

 of a wedge of London smoke glass an inch 

 square, and about a twentieth of an inch thick 

 at its blunt edge, a large low-power positive 

 eye-piece, and a special adapter, and is a very 

 convenient photometer to use. The color of 

 the wedge is deep enough to give one magni- 

 tude of the ordiuarj' scale of the brighter stars 

 for each five seconds in the time of extinction 

 at the equator. 



For the study of the accnracj' of obser- 

 vation with this instrument, I selected the 

 Durchmusterung star 22°. 2164, of which Ar- 

 gelander puts the magnitude at 5.3. In obser- 

 vation I took alternate observations on this, 

 and the star to be compared with it, until I 

 had five for each star, which I called a set of 

 observations. Bj' this method I made the con- 

 ditions of observation as nearlj' as possible 

 the same for the two stars, and thus the differ- 

 ence in their time of extinction nearly free from 

 error. 



My comparisons were made chieflj'' with the 

 star Durchmusterung 22°. 2163 of the cata- 

 logued magnitude 8.8. Between April 2 and 

 April 29 I made twentj'-eight sets of observa- 

 tions on the two stars. The difference in their 

 time of extinction varied from 19.1 seconds to 

 21.6 seconds; approximating, however, pretty 

 closely to the mean 20.6 seconds, of which 

 the probable error was ±0.09 in seconds, equiv- 

 alent to ±0.015 in magnitudes. The mean 

 error of a single set of observations is ±0.68 

 seconds, or ±0.12 magnitudes. A series of 

 four sets of comparisons of star 21°. 2156 gave 

 a mean error of ±0.68, and a probable error 

 of ±0.23; and a series of five sets with 

 21°. 2156 gave ±0.83 and ±0.24, in both cases 

 in seconds. 



