SCIENCE-GOSSir 



57 



CONIH!! Il'.n IIV K. smi l.INGTON «CAI.KS, l-.K.ll.S. 



Succ.KSTEl) Ll«T or I'o.Nos. — A corres|X)n(lcnt 

 writes lo us sii{;j;eslin(j that considering the almost 

 univiTsal interest taken tiy niicrosciipists in pond life, it 

 would lie iisefid if a list of productive ponds and 

 the specimens likely to be found there, were to be 

 published in these columns, and also that sujjgcstions 

 might be t;iven n\onthly for the maintaininj; of 

 aquaria. We shall bej^lad to carr}' out this proposal, 

 if possible, and hope some of our readers will write, 

 f^ivinp their brother workers the benefit of their 

 knowlerlge and experience in this respect. We are 

 now in the middle of summer, when pond-hunters are 

 busiest, and letters on the subjt>ct shouUl reach us 

 promptly if they are to be of service. The readers of 

 Si'lKNiK-dossu' have always been ready to help each 

 other, the)' have here an excellent opportunity. In 

 the meantime we may call attention to a well-known 

 little book by Mr. Henry .Schcrren, entitled " I'onds 

 and Kock I'ools," as well as to the older volume by 

 Mr. II. \. Slack on the " Marvels of Pond Life." 

 Both these little books have merit in being inexpensive, 

 as well as practical. 



Chas. Baker's Nkw CviAi.or.t'K. — Mr. Cha.s. 

 Baker has sent us his new and enlarged catalogue 

 which is a great improvement on former issues. Mr. 

 Baker lists and illustrates not only his own well-known 

 microscopes, but those of Zeiss, Leitz, and Reichert. 

 A great many slides aie included, but the prices of 

 these are, we think, in most cases, somewhat high. 

 Attention has been called in a former i,ssue of this 

 journal, to this firm's slide-lending department. .-\ 

 noticeable feature is the exceptionally complete series 

 of stains and reagents prepared by the ntost scientific 

 methods. There is a special catalogue of the 

 necessary apparatus for the study of the eft'ects of 

 malaria upon the blood, bacteriological outfits, etc. 

 The preface states that microscopes are included that 

 are suitable for engineering, brewing, baking, paper- 

 making, and other industries, but the suggestion that 

 a dissecting microscope, and " if anything more than 

 this be retpiired " a binoctdar microscope, fulfils the 

 requirements of the scientific papermaker, scarcely 

 >hows an intimate knowledge of the retjuirements of 

 that particular branch of manufacture. 



ClRlflT SlAlIK "\'AN IlKfKi k" M Ic Ki ISIOI'K. — 



Messrs. Watson and Sons have recently put upon the 

 market a modification of their well-known " Van 

 lleurck" microscope, which, by allowing more room 

 between the stage and the body, gives complete 

 rotation to the former. This is a step in llie right 

 direction. It has always appeared ridiculous that 

 costly and elaborate micro.scopes of this sort should 

 be, as we have seen them, sent out with mechanical 

 stage, centering adjustments, graduated divisions for 

 rotation, and even r.ack and pinion for thesame purpose, 

 yet incapable of rotation for more than, say. 27odeg., 

 through the screw heads of the mechanical stage 

 fouling the body of the in.strument. We hope other 

 makers of similar instruments will follow so good an 

 ex.miple. 



X^ 



N.A X^ 



mho on. 

 0\\ Immfksion 



COMiBNSIiR. 



(Jii, I.MMKRsin.N CoNliKNSKK. — Mcssrs. WatWJn 

 and .Sons, of High IlollKjrn. have sent for our inspec- 

 tion one of their new " rarachroinalic Oil Iinnicrkion 

 Condensers." We have examined this critically, and 

 are able lo siK-ak in the highest terms of its |K.Tform- 

 ance. < lur readers will be aware that for an objective 

 to work at its best the a|>erture of the condenser 

 shouhl approximate to that of the objective. Though 

 it is not every objective that will stanil so large a cone 

 of light, the best of our immersion lenses need a larger 

 aperture of illumination than the 170 deg. or so, that 

 can nominally be pas.sed through 

 them with an ordinary dry 

 achronuitic condenser. The to- 

 tal aperture of this condenser is 

 1 . 35 N. .A. , and its aplanalic aper- 

 ture isl)etween 1.25 and 1.3 N..\. 

 The clear aperture of the back 

 lens is 6 10 inch, and the power 

 of the condenser is ecpiivalent 

 10 an objective of ] inch focus. 

 It works through a slip 1 75 

 millimetres thick, and the 

 makers state that to |get the 

 best results the lamp should 

 not be less than 5 inches, or more than 7 inches 

 from the back of the lens. With this condenser 

 and a fine achromatic immersion objective of 

 similar aperture, we nave obtained results that 

 clo.sely rival the apochromatics. We think it will, 

 therefore, soon be looked upon as an essential part of 

 the outfit of the student of bacteria, the diatomist and 

 others. The price is so moderate as to bring it w ithin 

 the reach of most microscopists. Ihe optical portion 

 only, with universal objective thread, as illustrated, 

 costs ^'s, whilst the whole mounted with iris 

 diaphragm, graduated to show aperture in u.se, 

 stops, and revolving carrier is £,(i lOs. 



.Microi'1iotoi;rai>hy with Portrait Lens. — I 

 enclose a photograph of a grain of barley, taken with 

 the object of making a lantern slide, showing the 

 growth of the roots in malting. It is an instance of 

 what can be done in very low power photomicro-. 

 graphy with a portrait lens, and ordinary half-plate 

 camera. The lens used was a Dallmeyer patent 

 Stereo, working at f. 4, but I believe any good 

 portrait lens would have been equally efficient. The 

 barley was stained with methyl-green in order to get 



rid of the diffi- 

 a pale yellow ob- 

 on a white ground 

 piece of opal glass 

 plate with the em- 

 t h e n photo- 

 sanie wa\' that an 

 be copied. The 

 was illuminated 

 an acetylene 

 other with the 



i 



culty of taking 

 ject successfully 

 and fixed on a 

 an Ilford opal 

 idsion cleaned off 

 graphed in the 

 engraving would 

 grain of barley 

 on one side with 

 lamp, and on the 

 gaslight of the 



room, the object being to get a slight shadow on one 

 side, so as to give an effect of perspective to the picture. 

 The plate used wasaLumiereyellow green orthochroma- 

 tic. and the exposure was twenty minutes. It is often 

 desirable to take photographs and make lantern slides 

 of objects requiring only a \ery low magnification, and 

 it may interest your readers lo know that in this way 

 such photographs can be successfully obtained. The 

 magnification is about 2i times. — A'. C". Nelson, ig, 

 Kokcr Terrace, Sunderland. 



New Microscoi'E TROtu-.ii. — The vexed question, 

 of keeping fairly large aquatic objects alive under the 

 micro.scope, for an indefinite period, h.as yet lo be 

 solved. Perhaps the following suggestion will lead 



