SCIENCE. 



305 



ASTRONOMY. 



SWIFT S COMET. 



Swift's periodic comet, which has now become quite 

 faint, was observed on December 10th and nth, with the 

 26 in. equatorial of the Naval Observatory, and it is hoped 

 that more observations will be obtained as soon as the 

 moon has passed. On account of an elliptic motion, it 

 has been slowly departing from the ephemer's computed 

 by Mr. Upton with parabolic elements and published in 

 Vol. I, No. 2i, of " Science." 



The following is a continuation of Mr. Upton's ephe- 

 meris, which he has correced, however, from the most 

 recent observations : 



Ephemeris. — Washington Mean Midnight. 



date. 



11. 



December 18 5 



20 5 



22 S 



24 5 



26 S 



R. A. 



I>ECL. 



M. 



s. 







14 



44 



+ 38° 



S 2 ' 



20 



40 



3& 



45-1 



25 



53 



35 



29.9 



30 



35 



34 



19 .6 



34 



-17 



33 



14 .0 



A NEW Astronomical Journal, Urania, edited by Dr. 

 Ralph Copeland and Mr. J. L. E. Dreyer, is to appear 

 early in January. It will be published in numbers of from 

 16 to 24 quarto pages, as material can be accumulated. 

 The names of the editors, Mr. Dreyer as a former assistant 

 to Lord Rosse, and Dr. Copeland as Lord Lindsay's as- 

 sistant, are sufficient assurance that this will meet the 

 want long felt in England and Ireland of a journal, pub- 

 lished at frequent intervals, especially devoted to the in- 

 terests of astronomers. 



Lieut. S. E. Tillman, of the Corps of Engineers, whose 

 name is well known in connection with the American 

 Transit of Venus Expedition to Tasmania, has been ap- 

 pointed Professor of Chemistry, Mineralogy and Geology, 

 at West Point, in the place of Professor H. L. Kendtick, 

 who has voluntarily retired in order that this appointment 

 might be made. Professor Tillman has had a very varied 

 experience as an officer of engineers, his duties having 

 led him to astronomical and geodetic work in the field 

 and to geographical and geological explorations. The 

 military academy may be congratulated upon having 

 secured a valuable addit'on to its present s'rong academic 

 staff. 



The volume of Washington Astronomical Observations 

 for 1876, containing, in an appendix, the reports on the 

 toial solar eclipse of 1878, is expected, in a few days, 

 from the Government printing office. 



Mr. S. C. Chandler, Jr., publishes, in Science Observer, 

 a descrip.ion of an instrument, the " Almacantar," which 

 he has invented for determining time and latitude. The 

 instrumem is designed tor the observation of " Equal 

 Altitudes," the principle upon which it is made beino- 

 that of Kater's floating collimator. The Y's, in which 

 the pivots, rest are secured to opposite sides of a hollow 

 iron rectangle which floats in a rectangular basin of mer- 

 cury. The u lescope can be clamped in altitude and the 

 whole instrument rotated about a vertical axis. The 

 float is allowed to seek its level, and thus the telescope 

 will indicate t-qual altitudes on either sideof the meridian. 

 The 1 ;ror of a clock correction, as determined 



from-, observations with this instrument, is about 



fc 0.05 w. c. w. 



) J . S. — For notice of a new comet see page 297. 



To the Editor of Science: 



I observe what appears to be some errors in "dates in 

 the list of minor planets discovered by the late Prof. J. C. 

 Watson, mentioned by your correspondent. 



(133) Cyrene was discovered August 14, 1873. {Am- 

 erican Journal of Science, III., vi, 296). 



(174) Phaedra was discovered August 8, 1877." {Am- 

 erican Journal of Science, III., xiv, 325). 



(175) Andromache was discovered September 2, 1877. 

 {American Journal of Science, III., xiv, 325).. 



He also discovered, October 20, 1857, the planet ob- 

 served a few days before by Luther, and since named 

 Aglaia; also, October 9, 1865, the planet seen' by Peters 

 a few days previously, and since named Io; also, July 29, 

 1873, a planet which on account of cloudy weathe, 

 eluded his subsequent observation. {American Journal 

 of Science, III., vi, 296). 



A. WlNCHELL. 



University of Michigan, Ann Harbor, Dec. 11, 1880. 



MICROSCOPY. 



In the American Monthly Microscopical Journal for 

 December, Dr. J.J. Woodward claims for Professor J. L. 

 Riddell, M. D. of the United States, the priority in invent- 

 ing at least two forms of Binocular Microscopes, since 

 introduced by Beck of London, and Nachet of Paris. 



This communication of Dr. Woodward appears to prove 

 beyond a doubt that to an American, Dr. Riddell, then of 

 New Orleans, is due the credit of first demonstrating and 

 publishing the optical principle, on which all the most suc- 

 cessful binoculars, made prior to the present year, depend. 

 He first showed that the cone of rays proceeding from a 

 single objective may be so divided by means of reflecting 

 prisms, placed as close behind the posterior combination of 

 the objective as possible, that orthoscopic binocular vis on 

 can be obtained both with the simple and compound mic- 

 roscope. 



While giving full credit to Dr. Riddell for all that is due 

 to him, we think, in justice to Mr. Wenham, the fact 

 should be admitted that he was the first to produce a bi- 

 nocular arrangement for the microscope, so simple and per- 

 fect in its form, as to render its general use possible. We 

 once asked a London microscope maker, why the Stephen^ 

 son form of binocular was only adopted by a very few 

 microscopists, and were informed, in reply, that the ex- 

 pense was great in constructing microscopes on this model, 

 and on that account they were not popular. 



As we find from Dr. Woodward's paper that the im- 

 proved form of Dr. Riddell and that of Stephenson were 

 practically alike, it may be that for this the reason neither 

 received the attention anticipated. 



An interesting paper on Cercaria hyalocanda, by Herman 

 C. Evarts, may be found in the same Journal. This larval 

 form of a trematode was observed to come, from the com- 

 mon pond snail {Physa heterostropka) when placed in a 

 shallow dish containing water. 



In form, the body when contracted was globular, and 

 this form was maintained by the animal while actively 

 swimming about ; at rest it would extend its tail, and then 

 assume a somewhat triangular form. 



They were sufficiently large to be seen by the naked eye, 

 and were observed to encyst themselves, contracting during 

 the process to a globular form, around which was secreted 

 a glutinous mass. A few seconds after the cyst commenced 

 to form, the tail detached itself and swam away. 



We arc also indebted to this journal, for the descrip- 

 tion of the following method of mounting opaque objects, 

 contributed by Mr. A. II. Chester: — 



" The object is first fastened to the slide, which is centered 

 on the turn-table, by means of a weak solution of gelatin, 



