284 



SCIENCE. 



flector, being fully as bright on that date as at any pre- 

 vious observation, although its theoretical brightness is 

 decreasing. It is a faint, diffused object, but to show 

 that it is within the range of quite moderate telescopes, I 

 would say that I first picked it up on the evening of No- 

 vember 5th, with a refractor of only two inches aperture. 

 In my last observation two faint stars were seen shining 

 through the comet. 



The comet's position for the 10th of December will be 

 A. R. 4 hours 40 minutes, Dec. + 44 degrees 47 minutes. 

 On December 14th it will be about 5 degrees south of 

 Capella. William R. Brooks. 



Red House Observatory, Phelps, N. Y., 

 November 30th, 1880. 



MICROSCOPY. 



Dr. Carpenter, the well-known English microscopist, oc- 

 cupied the attention of the Royal Microscopical Society, 

 on the 6th instant, by describing the "Student Micro- 

 scope," recently designed by Mr. George Wale, of New 

 Jersey. The instrument in question was highly com" 

 mended for its efficiency, and English opticians were 

 advised to consider the practical improvements it suggests. 



Mr. James Swift exhibited and described an improved 

 form of Calotte diaphragm, consisting of a series of small 

 circular apertures, to be applied above the achromatic 

 condenser immediately beneath the object, and on a level 

 with the surface of the stage. 



A binocular eye-piece, by Professor E. Abbe, was de- 

 scribed as consisting of two uncemented prisms (together 

 forming a thick plate of glass) in the direct tube ; the ad- 

 jacent diagonal surfaces of the prisms being both cut at 

 the calculated angle of 38 5', which angle was computed to 

 allow precisely one-half of the light to be transmitted, and 

 to reflect the other half ; the latter half fell upon a total re- 

 flecting prism, whence the rays emerged through the 

 diagonal tube to the left eye. Another point was the 

 mechanism by which the diagonal tube attached to the 

 direct tube by a box-fitting, was moved to accommodate 

 the width of different observer's eyes, a screw motion 

 causing the tube, with eye-pieces above and reflecting 

 prism below, to travel smoothly nearer to or further from 

 the direct and stationary tube. 



The application of the eye-piece to the left tube at such 

 a distance as to compensate for the extra distance travelled 

 by the pencil of light, and thus render the images seen by 

 both eyes of equal magnitude. 



Lastly, the application of two semi-circular caps, one 

 over either eye-piece ; in one symmetrical position of these 

 apertures the effect produced was pscudoscopic vision, by 

 another arrangement of them stereoscopic vision was ob- 

 tained. 



This form of binocular is said to be specially appli- 

 cable to the short tubes of Continental microscopes and 

 some of American make, 



A new fluid for writing the names of objects on glass 

 slides is sold by Mr. Browning, of London. It is more active 

 than hydrofluoric acid, and has an immediate action on the 

 surface of >zl;iss. 



Dr. Giinther, of Berlin, has made photographs of Frus- 

 tulia Saxonica. These and a micro-photograph by Mr. S. 

 Wills, of Boston, were compared with the' photograph by 

 Dr. Woodward, produced in 1875. The latter showed no 

 trace of beaded resolutions, whereas both the former showed 

 the resolutions remarkably well. Mr. Mayall asks if Dr. 

 Woodward still maintains his opinion of the unreality of 



the longitudinal lines. 



Mr. Crisp mentions that Professor Abbe has found great 

 atage ill mounting diatoms in monobromidc of naph- 

 thaline, by which they were rendered far more visible than 

 when mounted on Canada balsam. 



BOOKS RECEIVED. 



The Naturalist's Directory for 1880. Edited 

 by Samuel E. Cassino, 299 Washington street, 

 Boston. May, 1880. 



This useful work will be welcome in scientific circles ; 

 it contains the names, addresses, special departments of 

 Study, of Naturalists, Chemists, Physicists, Astronomers, 

 etc., etc., etc. It also gives a list of scientific societies, 

 of scientific periodicals, and the titles of scientific books 

 published in America from July I, 1879 to October 1, 

 1880. 



The arrangement of the names in this edition of the 

 directory ts by States, and was adopted after repeated 

 requests, though not, as the publisher admits, without 

 misgivings on his part as to the convenience of the 

 list thus arranged. On this point we are glad to notice 

 that what we consider to be an error is acknowledged, 

 and that in future the alphabetical order will be resumed. 

 For our purposes the directory thus arranged is almost 

 useless, as the loss of time in searching 45 separate lists 

 for an address, is a great drawback to the use of the 

 work. 



We are also at a loss to know on what principle the 

 list has been constructed, as the omission of the names 

 of well-known scientific men is quite incomprehensible ; 

 as examples we fail to notice Professor John Le Conte, of 

 California; Professor W. H. Brewer, of Yale; Professor 

 Jas. D. Dana, of Yale ; Professor Simon Newcomb, ot 

 Washington ; Col. J. J. Woodward, M. D., Washington ; 

 Professor Asaph Hall ; Professor Julius E. Hilgard, 

 Washington ; Professor C. Y. Young, of Princeton ; Pro- 

 fessor C. F. Chandler, of New York City ; Professor 

 Henry Draper, of New York City ; and Professor Jno. 

 W. Draper, of Hastings-on-Hudson, or Mr. Edison. We 

 have had no time to make a systematic search for omis- 

 sions, but the above names which are household words 

 in scientific circles do not appear. 



As we find some of these names have already appeared 

 in previous editions, the present omission would not 

 appear to be altogether accidental. 



As this directory is the only one of its kind published, 

 we suppose these errors will not effect its sale, but we 

 regret that a more perfect work was not produced. 



Since writing the above notice, we have heard from the 

 publishers of the Directory ; they state that the arrange- 

 ment of the work is acceptable to a majority of the sub- 

 scribers, and that the cause of the omission of names was 

 due to their failure to receive responses to printed cir- 

 culars which were forwarded to all known scientists. 



The readers of this journal must be familiar with the 

 efforts we have made to secure a perfect register of the 

 scientific men of the United States. Our intention in 

 this respect was also made known by an editorial notice in 

 the New York Times, and in the Medical Record of last 

 week. 



The Times pointed out the value of such a perfect list, 

 and the little trouble it entailed on scientific men. So 

 far the response to our appeal has been very partial. 

 We therefore again request those who have hitherto 

 failed to forward their names and addresses, with special- 

 ity of study, to do so at once, and if the heads of Uni- 

 versities ani Colleges would make up lists, considerable 

 help would be rendered. 



We also suggest that those interested in scientific pur- 

 suits make up lists of scientific men in their neighbor- 

 ly iod, and of amateurs following a particular line of 

 scientific investigation. 



As we stated lists of names will be forwarded to the 

 Smithsonian Institution, and Messrs. Cassino and others 

 will have the full benefit of it for future use. 



