October io, 1895] 



NA TURE 



579 



arranged (with a few exceptions) in alphabetical order, while the 

 names follow the same order. Each name is followed by a full 

 address, and by an indication of the special branch or branches 

 of study in which the person it designates is interested. To 

 give an example of the scope of the contents, it may be said that 

 under London we find the names of the professors and assistants 

 in the zoological and kindred departments in the various colleges 

 and medical schools ; the staffs of the departments of zoolog)- 

 and geology in the Natural History Museum ; some of the mem- 

 bers of the Geological Survey of England and Wales ; a list of 

 the members of the Zoological Society ; the names and places of 

 meeting of a number of London and suburban scientific societies 

 interested more or less in zoology'; and lists of draughtsmen, 

 opticians, publishers, and of taxidermists and dealers in ani- 

 mals. In some cases the lists are much fuller than in others, 

 owing proba^jly to the fact that some colleges and institutions 

 furnished the publishers with more detailed lists than others. 

 But though a few names are omitted from the places where one 

 first looks for them, they can in most cases be found somewhere 

 in the volume. Very valuable is an index of the names arranged 

 in groups according to the subjects especially studied, and a 

 geographical index. And, finally, the personal index at the end 

 of the volume renders it possible to find the name, address, and 

 S|iecial work of any zoologist entered in the work in a few 

 moments. It is well known that the Germans excel in pro- 

 ducing directories of the kind before us, and, so far as we can 

 make out, the present work will sustain their reputation. Being 

 international, the directory will help to bring together observers 

 accumulated in widely separated regions of our globe, and so will 

 lead to a better knowledge of the world's fauna. We congratu- 

 late Messrs. Friedlander upon the enterprise they have shown in 

 ]>reparing and producing such a useful work ; and we hope the 

 time is not far distant when the designations of students and 

 investigators in the domain of physical science will be brought 

 together in a similar directory. 



The additions to the Zoological Society's Gardens during 

 the past week include a Black Ape ( Cynopithecics nigir) from 

 Celebes, presented by Mr. Frank Greswolde Williams; a 

 Rhesus Monkey {Macacus rhesus, <J ) from India, presented 

 by Mr. IL Small; a Bonnet Monkey {A/araiiis siniciis,^), a 

 Macaque yionVny {Macruiis cyiiomolgiis, 9 ) from India, presented 

 by Mrs. Lionel Smith ; a White-tailed Ichneumon (Herpesles 

 albuatida), two Blotched Genets (Geiielta tigriiia) from Natal, 

 presented by Mr. \V. Champion ; a Cape Hyrax (Hyrax 

 fapensis), two Suricates {Siiricata telradaclyla) from South 

 Africa, presented by Mr. J. E. Matcham ; two Norwegian 

 Lemmings (Myodes lemritus) from Norway, presented by Mrs. 

 1 laig Thomas ; a Passerine Parrakeet ( Psittamla passerina) from 

 Brazil, a Silky Cow-Bird (Molothriis bonarieiisis), a Red-crested 

 Cardinal (Paroaria aiaillata) from South America, presented 

 by Mr. R. Norton ; two Common Kingfishers (Alcedo ispida), 

 British, presented by Mr. J. A. Clark ; a Passerine Parrakeet 

 (Piillaiulapasariita) from Brazil, a Tuberculatcd Iguana (Igttana 

 tiihniilala) from the West Indies, two Common Teguexins 

 ( Tiipinambis tegtiexin) from South America, deposited. 



OUR ASTRONOMICAL COLUMN. 

 Measurement ok Planetary Diameters.— In a paper 

 givmg particulars of measurements of the polar diameter of 

 Mars (Astronomical Journal, No. 354), Prof Campljell gives 

 an mterestmg summary of the conditions of planetary measures 

 in general. He points out that measurements of diameter are 

 affected by a variety of errors, among them being spherical and 

 chromatic aberration, imperfect atmospheric condition.s, irradia- 

 tion, diffraction, and imperfect focus, all of which tend to 

 increase the apparent diameter of the object; while, in addition, 

 NO. 1354, VOL. 52] 



personal equation and accidental errors may also affect the 

 results. The effects of spherical and chromatic aberration, a.s 

 well as of diffraction, may be regarded as constant throughout 

 a series of measures of any given object. Differential refraction 

 can be satisfactorily corrected for, but the irregular refraction 

 caused by the unsteadiness of the atmosphere, and resulting in 

 "poor seeing," may produce very large errors indeed. The ap- 

 parent increase of diameter due to irradiation may be regarded 

 as sensibly constant with any given telescope, eyepiece, planet, 

 and background. Imperfect focus may produce considerable and 

 variable errors ; in the 36-inch Lick telescope, an error of a 

 thousandth of an inch in focussing increases the diameter of a 

 planet by o"-02. Experiments as to the best method of pro- 

 cedure were made by Prof. Campbell in June and July, 1894, 

 with the result that the f(jllowing programme was adopted in the 

 case of Mars : (a) All the observations were made with the sun 

 above the horizon, and the advantages of a bright sky background 

 were very marked ; it was believed to reduce all the errors, 

 except possibly that of personal equation. (*) Obser%ations were 

 only made in a tranquil atmosphere, (c) The same eyepiece was 

 used throughout. (d) An eyepiece cap with a very small 

 aperture was employed. («■) The observers eyes were always 

 similarly situated with respect to the threads of the micrometer. 

 (/) The micrometer threads were always placed parallel to the 

 great circle passing through .Mars and the sun. [g) The micro- 

 meter threads were placed directly upon the opposite limbs of the 

 planet. 



Following this programme, and adopting \'oung's value of 

 1/2 19 for the polar compression, the most prolrable polar 

 diameter of Mars, at distance unity, was found to be 9" -25-1- 

 o"oi2, while the equatorial diameter resulting from the measures 

 was 9" 30. 



The Craters on the Moon.— Much has been learnt about 

 the configurations of the lunar surface since the idea of examin- 

 ing very greatly enlarged photographs came into practice. It 

 was only natural, however, that many interested in the subject 

 should have looked upon the interesting results of Dr. Weinek 

 with scepticism, for it was hard to believe that such detail structure 

 could be so perfectly secured on the photographic plates. Such 

 doubts as to their existence were somewhat increased by the fact 

 that many details were invisible to eye observations, or at any 

 rate were thought to be, but the fact was not sufficiently grasped 

 that the photographic plates showed only the detail as it appeared 

 at the moment of the exposure, which might have differed con- 

 siderably from that which preceded it or, followed it by a few- 

 seconds. 



Every confidence is now placed in the photographic records, 

 and under suitable and similar observing conditions the eye 

 should be ably to verify them directly. M. C. .M. Gaudiben, in 

 Atr. Nach. No. 3310, tells us of his discovery, with an instru- 

 ment of 260 m.m. aperture, by eye observations alone, of a small 

 crater only Soo metres in diameter. It lies on the top of the 

 central mountain of Albategnius. This crater has been subse- 

 quently found by Dr. Weinek on a negative taken by MM. 

 Loewy and Puiseux 1894, February 13, 4h. 6m. Mean Time 

 Paris. 



A diligent search by M. Gaudibert has also enabled him to 

 secure the necessary observational conditions to see the two 

 small craters discovered by Weinek near the crater and to the 

 east of the Rephees mountains. 



Suggestion i-or Astronomicai. Research. —Dr. Isaac 

 Roberts draws attention to a piece of useful astronomical work 

 which may be performed by those who take a practical interest 

 in the subject, namely, to determine what changes, if any, have 

 taken place among the stars in the regions photographed by him 

 at intervals during the past eight years. In the first instance it 

 will only be necessary to compare the earlier photographs pub- 

 lished in his well-known " Photographs of Stars, Star Clusters, 

 and Nobuke " with the new series now appearing in Knauiled-re ; 

 but arrangements are being made which will enable investigators 

 to refer to glass positives, or the negatives themselves, to settle 

 any doubtful points. The photographs being enlarged to the 

 same scale, comparative measurements may readily be made by 

 means of a n'seaii ruled on glass, and a transparent protractor 

 will enable position angles to be determined. The scale of the 

 l>h(jtographs is such thai any change of position exceeding three 

 seconds of arc may be detected by careful measurements. 

 "Thus, a system of astronomical research would be inaugurated, 

 that must eventually add largely to existing knowledge." 



