886 



SCIENCE. 



[N. S. Vol. XXIII. No. 597. 



stars whose brightness is greater than that cor- 

 responding to magnitude zero, and suggests 

 instead the word supermagnitude. The sun, 

 therefore, becomes 26.59 supermagnitude. 

 This value is based upon the Potsdam magni- 

 tudes of Polaris, Alpha Canis Min., and 

 Sirius, which are 2.15, 0.56 and — 1.09. The 

 corresponding Harvard magTiitudes are 2.12, 

 0.48 and — 1.58, the use of which would, of 

 course, have led to slightly different results. 

 The sun sends us about seventeen billion 

 times as much light as Sirius, the brightest 

 star in the heavens. 



RECENT AND COMING TOTAL ECLIPSES OF THE SUN. 



The total eclipse of August 30, 1889, was 

 in many respects a favorable one. Skilled ob- 

 servers from various countries took up sta- 

 tions at so many widely separated places along 

 the belt of totality, that the phenomenon 

 could not well escape them all. Although 

 clouds prevented observations in Labrador, 

 elsewhere — in Spain, Algeria and Egypt — ob- 

 servations and photographs were obtained, 

 which should increase substantially our knowl- 

 edge of the sun, when the results have been 

 reduced and compared. 



Professor David P. Todd and Mr. E. H. 

 Baker, of the Amherst Observatory, have is- 

 sued a pamphlet, calling attention to the next 

 favorable eclipse. Although there will be six 

 total eclipses during the next six years, that 

 of January 13-14, 1907, seems to be most 

 favorable. This eclipse, however, presents 

 some difficulties, since the track of totality 

 lies in Turkestan and Mongolia. Neverthe- 

 less, it will doubtless be observed by some en- 

 thusiastic astronomers. The duration of 

 totality will be about two minutes. 



S. I. Bailey. 



FLUID LENSES. 

 A REPORT from Consul-General W. A. 

 Kublee, at Vienna, states that after experi- 

 ments extending over a number of years a 

 Hungarian chemist has succeeded in producing 

 optical lenses by a simple and cheap process 

 that are not only quite as good as the best 

 massive glass lenses at present used, but that 

 can be manufactured of a size three times as 



great as the largest homogeneous glass lens 

 heretofore made. 



The importance of this invention in the 

 field of astronomy is obviously very consider- 

 able. The largest glass lens heretofore manu- 

 factured out of massive glass for astronomical 

 purposes has a diameter of about 1.50 meters, 

 and it required several years to make it, while 

 the price was several hundred thousands of 

 marks. Such a lens can be manufactured by 

 the new process in a few weeks at a cost of 

 2,000 or 3,000 marks. The price of a glass 

 lens of the best German manufacture, with a 

 diameter of 25 centimeters, is now about 7,000 

 marks, whereas the price of a similar lens 

 made by the new process is about 150 marks. 

 Lenses of smaller diameter for photographic 

 purposes, for opera glasses, reading glasses, 

 etc., can be produced at correspondingly 

 smaller cost. The lens consists of a fluid 

 substance inclosed between two unusually hard 

 glass surfaces, similar to watch crystals, in 

 which the refractive power and other charac- 

 teristic properties are so chosen that the glass 

 surfaces not only serve to hold the fluid, but 

 also combine with the fluid to overcome such 

 defects as are scarcely to be avoided in ordi- 

 nary lenses. It is for this reason also that 

 the lens is achromatic. 



The fluid contained in the lens is hermet- 

 ically closed, so that no air can enter and ex- 

 ercise a damaging effect. The fluid does not 

 evaporate, and its composition is such that its 

 properties are not aSected by time or by tem- 

 perature. The coefiicient of expansion, both 

 of the glass and of the fluid, is approximately 

 the same between the temperatures of 15 de- 

 grees of cold and 60 degrees of heat. Another 

 advantage of the lens is that, on account of 

 the fact that the fluid is not dense and the 

 glass crystals are thin, the whole lens com- 

 bination through which the light must pene- 

 trate is very slight. 



These fluid lenses are already manufactured 

 in Austria, and are attracting attention both 

 on account of their utility and the small price 

 at which they are sold. Patents have been 

 taken out in other countries, and they are 

 soon to be introduced. 



