446 



KNOWLEDGE & SCIENTIFIC NEWS. 



[June, igo6. 



Enlarging. 



If astronomical photography is to I)c seriously en- 

 firajjcd in, pro\ision must be made for enlarginiif the 

 prijjinal not^ativc, in order that tlie details of small ob- 

 jects may be siiown on a larg-er scale. The usual method 

 of projection by a lantern is unsuited for delicate astro- 

 nomical work, and an enlarging camera, similar to 

 that shown in dealers" catalogues, should be employed. 

 These are provided with a long bellows body having a 

 division at the centre for the support of the lens. The 

 front portion should be fitted with carriers suitable for 

 the various sizes of plates there may be occasion to use. 

 The other end should be provided with a focussing 

 screen of a suitable material, and a dark-slide with 

 carriers to take whole, half, and quarter plates. 

 Almost any lens which gives a perfectly flat field when 

 stopped down may be employed. The negative should 

 be covered with a piece of ground glass to diffuse the 

 light, and the whole arrangement placed in front of a 

 window. -Slow plates should be used, and it is strongly 

 recommended that these bo de\ eloped with glycin as 

 previously described. 



If the enlarging operations can be carried out in a 

 dark room a camera may be dispensed with altogether. 

 L'nder such circumstances it will only be necessary to 

 place the negative in an opening in the window, while a 

 baseboartl with a support for the lens, and another for 

 the plale, or papet , as the case may be, is all that is 

 required in the shape of apparatus. 



Further details need not be entered into here, as 

 these m:iy be found in any photographic text-book, but 

 there is one feature in connection with enlarging, which 

 may be brought under the notice of those engaged in 

 scientific work. If it is desired, for example, to en- 

 large a small image up to, say i6 diameters, and if this 

 is done at one operation, the grain of the plate will be 

 so obtrusive that there may 1k' a difficultv in some cases 

 in mentally separating the objective details of the image 

 from effects which are spurious. No silver image will 

 bear direct enlargement to the extent in question, and 

 to get the best results this should not be carried further 

 than two diameters at one operation. Four exposures 

 are, therefore, necessary, a positive and negative image 

 being used alternately. The advantage of this method 

 will be at once apparent. Instead of spreading the 

 original image over an area 256 times in extent, a fresh 

 film with the requisite amount of density is obtained at 

 each exposure. 



The Gypsy Moth in America. 



A curious instance of the adjustment of a newly introduced pest 

 to its surroundings is reported in the last proceedings of the 

 liiological Society of Washington. In the year 1868 some breeding 

 oxjieriments were being made in the Washington Laboratory with 

 tlm European " gypsy molh." By some accident an "egg ma=s " 

 W.1S lost — got loose in fact. The consequence was that in the next 

 year Massachusetts found itself faced with a gypsy moth invasion. 

 After spending ;f2oo.ooD in fighting the insect, the State of Massa- 

 chusetts gave up the task, and the moth immediately began again 

 to gain ground. Last year the State appropriated another £60,000 

 to be spent during the following thrte years in a new scientific 

 attempt to stem the ravages of the moth. Of this sum £2,000 is 

 being spent in the introduction of the parasites which in Europe 

 prey on the moth, and from Sardinia 2.500 parasite-infested larva; 

 have been intioduced. Developments are now being anxiously 

 awaited. The gyp y moth is attacked by .Vmerican parasites, but 

 it seems to be able to deal with Ihem better than with the 

 European variety, and its own vitality is greater in the New World 

 than the Old. 



The Royal Society 

 Soiree. 



The first of the two scientific .soirtks annually given by 

 the Royal Society in their apartments at Burlington 

 House was held on May 9 last, and attracted a repre- 

 sentative gathering. The programme of exhibits, cm- 

 bracing as it docs on these occasions something from 

 practically every department of science, marking either 

 novelty or progress is, naturally, of too extended a 

 character to permit more than a brief notice. Allusion 

 may, hov\ever, be made to a few specially noteworthy 

 features, while we are privileged at the same time to 

 proxide the welcome supplement of a selection of illus- 

 trations. ■ 



The astronomical exhibits were particularly interest- 

 ing and admirably shown, the use of the " linolitc " 

 system of electric lighting being effectively drawn upon 

 to illuminate the .scries of transparencies. Father 

 Cortie, of Stonjhurst, .sent his photographic plates 

 illustrative of the total solar eclip.se of 1905, August 30, 

 taken at X'inaroz, on the coast of Spain. In the.se the 

 chief features are the striking group of prominences, 

 the arches and a \ortex ring o\er the prcminences, 

 bright rays and streamers, and a dark ray and plumes; 

 the latter .seem to converge to a position previously the 

 seat of the great sun-spot of February' and March, 1905. 

 Fciipse results were also furnished by the Astronomer 

 Royal and Sir Not man Lockyer. The Royal .\stro- 

 nomical Society sent six splendid photographs of the 

 Milky Way galaxy, taken last year by I'rof. E. E. 

 Barnard at ]\Iount Wilson, California. 

 ■ In the department of electricity Mr. Kenneth J. 

 Tarrant's set of photographs of electric discharges at 

 atmospheric pressure and in vacuo attracted much at- 

 tention. In these were .seen the results obtained from 

 an interrupted continuous current, and from a high 

 frequency oscillating one, also between parallel con- 

 ductors, both insulated and bare; of \arying capacity 

 and with various condcn.ser conditions. The spiral 

 formation of high frequency discharge, and the same 

 feature in a vacuum a little short of that necessary for 

 the Riintgen phenomena was clearly shown in some cf 

 the photographs. 



The first of the two photographs reproduced here shows 

 a simultaneous discharge from both poles of a 10-inch 

 coil on to the same plat2, the current through the 

 primary being reduced so as to keep the discharge 

 within the limits of the plate. Here is presented the 

 final result of a number of experiments under various 

 conditions, to ascertain whether the marked difference 

 ob.served in the character of the figures obtained from 

 the twO' poles of an induction coil was real, or only 

 'due to the static induction of the photographic plate 

 itself, or other varying conditions. The second photo- 

 giaph shows an oscillating discharge from a non-mag- 

 netic transformer, between two parallel wires of eqiuil 

 size. A spiral twist along the lines of discharge ap- 

 parently indicates rotation. 



Mr. Julius Rheinberg's exhibit of photo-micrographs 

 taken by Dr. \. Kiihlcr with ultra-violet light bv means 

 of his specially designed Zei.s,s apparatus, was of great 

 interest, as well as the allied demonstration by 

 M€.ssrs. Beck, Ltd., of the ultimate microscope re- 

 solving power with light of different wa^■e-lengths. 

 For the diatom specimen which was shown in ex- 

 emplification, a i-i2th-inch oil-immersion objective was 

 u.sed. Hie beam of a Xernst lamp was split up into a 



