August 23, 1906] 



NA TURE 



417 



brinf< scientific knowIed{<e, in a popular form, before socie- 

 ties unable to pay large fees for professional lectures, and 

 all fees paid for lectures are devoted to the working 

 expenses of the section. Applications for the list by the 

 secretaries of natural history and kindred societies should 

 be made to the honorary secretary of the extension section 

 of the Manchester Microscopical Society at 22 Filey Road, 

 l"alli)\vfield, Manchester. 



Mkssrs. Wratten and Wainwric.ut have sent us a batch 

 of their panchromatic plates, which have been recently pre- 

 p.u-.-d in response to the demand for a plate having more 

 uniform sensitiveness to the various spectral colours. Very 

 searching tests on photographs of various spectral radiations 

 show conclusively the unique qualities of the new emulsion. 

 For instance, on a photograph of the spectrum of the iron 

 arc the green region, usually diflicult to obtain with such 

 expiisures as give the blue of normal density, is shown of 

 actually greater density than the blue ; at the same time, 

 the red end of the spectrum is very uniformly rendered up to 

 \ 7600, and with slightly longer exposure somewhat beyond 

 this. This particular batch of plates was of medium 

 rapidity, the sensitiveness measured to daylight being 

 1)4 II and D, 138 Watkins and F/c)4 Wynne, nevelopmcnt 

 look about 3 minutes for most of the exposures tried, and 

 the plates vi'ere clear and clean in working. An important 

 factor in spectroscopic work is the fineness of the grain of 

 the silver deposit, and in this respect the Wratten pan- 

 chromatic is excellent. There is no doubt that for spectrum 

 investigation extending over the whole region from ultra- 

 violet to extreme red these plates are the most satisfactory 

 at present obtainable. If one might be permitted to ask 

 for further convenience, it would be to maintain the 

 present colour sensitiveness ratios, and endeavour to in- 

 crease the general rapidity. Should it be found possible to 

 do this and, at the same time, keep the grain within 

 reasonable bounds, this type of emulsion would be of 

 immense service for stellar spectrum photography, as for 

 this purpose a rapid plate is essential on account of the 

 feebleness of the light. A notable feature of the instruc- 

 tions sent out with the plates is the provision (for the first 

 time, so far as we are aware) of a table showing the normal 

 time of development for varying temperatures. It is well 

 known that the temperature of the developing solution has a 

 considerable effect on the speed of appearance and subse- 

 quent growth of the latent image, and as the new plates are 

 practically equally sensitive to all colours, requiring de- 

 velopment in darkness, it is very advantageous to be 

 able to control by time the correct duration of the pro- 

 cess. The figures given for this purpose are not arbitrary, 

 but have been obtained from exhaustive experimental trials, 

 and can therefore be relied on without hesitation to give 

 comparatively uniform results. The developer recommended 

 is a very weak combination of metol hydroquinone, but 

 excellent results have been obtained with other ordinary 

 developers, some much more concentrated, so that no dif- 

 ficulty is likely to be found from this cause when the time 

 best suited to the developer chosen is once determined. 



Two more parts of Prof. O. D. Chwolson's " Traits de 

 Physique," which M. h. Davaux is translating into French 

 from the Russian and German editions, have been pub- 

 lished in Paris by M. \. Hermann. The first parts of 

 vols. i. and ii. were reviewed at length in our issue for 

 February 15 last (vol. Ixxiii., p. 362), and the present 

 fascicles are the second parts of these volumes. The former 

 deals with the gaseous state of bodies, and the latter with 

 indices of refraction and the dispersion and transformations 

 NO. IQ2I, VOL. 74] 



of radiant energy. As in the volumes reviewed on a previous 

 occasion, the two new parts are provided with notes on 

 theoretical physics by MM. F. and F. Cosserat. 



Prof. H. Erdmann's " Lehrbuch der anorganischen 

 Chemie," the fourth edition of which has just been pub- 

 lished by Messrs. F. Vieweg and Son, Brunswick, is a 

 comprehensive text-book containing nearly eight hundred 

 pages and three hundred figures. The work presents a 

 concise statement of the present position of inorganic 

 chemistry ; it should be of service, not only to students of 

 chemistry, but also to those concerned with the study 

 or progress of other branches of pure and applied 

 science. 



OVR ASTRONOMICAL COLUMN. 



("OMET iqofid. — Froin an observation made at Lyons on 

 July 21, M. J. Guillaume recorded that Finlay's comet, on 

 that date, had a nebulous appearance with diffuse edges, 

 and that the central condensation was of the twelfth magni- 

 tude, the magnitude of the whole object being 11-5. 



The observation also showed that the position given by. 

 M. Schulhof's ephemeris for that date needed but small 

 corrections ; a further abstract from the ephemeris is given 

 below : — 



Ephemeris {12)1. M.T. Paris). 





a(app ) 



5 (app.) 



log . 



1025 



966 

 9-08 



8-53 



-I- 14 31 ... 950197 



+ 15 18 ... 9 5'725 



+ 15 59 •■■ 9"53258 



+ 16 37 ... 9'54783 



The comet will pass about 1° south of 15 Orionis on 

 August 26 {Astro)ioniischc Nachrichlen). 



A Memorial to the late Prof. Tacchini. — From No. 7, 

 vol. XXXV., of the Mcmorie delta Societd degli Spettroscopisti 

 Italiani, we are pleased to learn that an international 

 subscription list has been opened for the purpose of found- 

 ing some lasting souvenir in honour of that great Italian 

 astronomer the late Prof. Tacchini. 



.\ circular letter to this end has, evidently, already been 

 addressed to the members of the society which he founded, 

 and a goodly sum thus realised, but not sufficient to 

 fulfil the object aimed at in a manner worthy of the 

 occasion. 



No doubt the fellow-workers and admirers of Pietro 

 Tacchini, who did so much for the cause of astronomy, 

 will be glad to have this matter brought to their notice, 

 and to help forward the scheine. Subscriptions should be 

 addressed to Prof. L. Palazzo, Directeur du Bureau Central 

 de M^tterologie et G(5odynamique, Rome. 



Report of the Paris Observatory for 1905. — .Although 

 M. Lcewy, in opening his report of the work done at the 

 Paris Observatory during the year 1905, mentions that 

 observations were curtailed owing to the preparations for 

 the total eclipse of the sun, the lamented death of M. Pau' 

 Henry, the necessarv alterations to the principal meridian 

 circle, and other causes, it appears from the report itself 

 that a great deal of work was prosecuted during the 

 vear. 



The publications included twenty-seven sheets of the 

 " Cart du Ciel " showing images of 39,697 stars, the ninth 

 part of the photographi'c atlas of the moon, the^ second 

 volume of the " Catalogue photographique du Ciel," giving 

 the rectangular coordinates of some seventy thousand stars 

 between declination +22° and -1-24°, and the Annales for 

 1902. 



Two important pieces of work, the determination of the 

 difference of longitude Greenwich-Paris, and the reduction 

 of the magnitudes and positions of the stars in the cluster 

 Messier 3, were completed. 



The programme for the current year includes, among 

 other things, the determination of the constant of aberra- 

 tion by M. Bigourdan, the measurement of stellar radial 

 velocities by M. Hamv, and the photographical record of 

 the ionisation of the atmosphere by M. Nordmann. 



