322 



KNOWLEDGE. 



August, 1911. 



this model obliquely and varying the angle at which the tubes 

 crossed, all the appearances of beaded, exclamation and 

 cuneate markings observed in the natural scales could be 

 exactly reproduced. — Mr. Murray: Further report on the 

 rotifera collected by the ShacUleton Antarctic Expedition of 

 1909. Rotifera of Nezc Zealand. There were collected 

 forty-one species of Bdelloids, and twenty-six species of other 

 orders. Three new species were described — CaUidina 

 iiiicrocornis, Rotifer ciirtipes and R. inoiitaiuis. A species 

 of Pedalion (not ideutilicdl occurred as a plankton animal in 

 a great lake tWakatipuL The Bdelloid fauna of New Zealand 

 appeared to be poor, considering the variety of conditions 

 found in different regions. Rotifera of S. Africa. During a 

 short stay at Cape Town nine Bdelloids were collected on the 

 lower part of Table Mountain. There was one new species. 

 Dissotroclta pcctinata. related to D. spinosa. This small 

 collection was noticeable for the absence of any of the species 

 characteristic of tropical and subtropical Africa, many of 

 which occurred in other parts of Cape Colony. 



Mr. Conrad Beck gave a demonstration of the method of 

 determining in wave-lengths the divisions of a stage- 

 micrometer by means of an interferometer. 



He said the interferometer consists of a series of mirrors 

 which receive a beam of light from a radiant somxe, and divide 

 it into two beams of light, which are afterwards re-combined 

 and viewed by a telescope. All the portions of the instrument 

 are fixed, except one reflecting mirror, which reflects one-half 

 of the divided beam of light. This can be set in such a 

 position that the two half-beams of light, during their period 

 of division and before they re-combined into one, ha\e 

 travelled exactly the same distance. .A movement of the 

 reflecting mirror can then be made, so that one half -beam of light 

 has travelled half a wave-length farther than the other ; and 

 when that is the case, interference will take place, and the 

 light will be extinguished. As the mirror is moved farther, the 

 light will again appear, until the path is one-and-a-half 

 wave-lengths different, when a second interference is produced : 

 this goes on at each successive motion of the mirror through the 

 same distance, and the wave-lengths are counted. 



As a matter of practice, it will be seen, on looking through 

 the telescope, that the effect is not a complete change from 

 brightness to darkness, because this only takes place in the 

 exact centre of the field, and a series of bright and dark 

 bands are seen in the field, which travel from right to left, 

 and are counted as they cross the centre of the field against a 

 line in the telescope. 



The apparatus was shown with a Bunsen burner and a 

 sodium flame as being a sufficiently monochromatic light 

 for demonstration ; but as the sodium light is not a purely 

 monochromatic light, but consists of two lines which are not 

 in themselves quite monochromatic, sodium does not form a 

 very good source for the illumination. Either cadmium, 

 mercury or hydrogen, used in connexion with a prism which 

 shall direct one only of the chief lines into the instrument, is 

 the best for the purpose. 



The micrometer is held on a bracket which projects out 

 from the carriage on which the moving mirror is l^xed in such 

 a manner that, although it is \ iewcd by the microscope, it is 

 not in contact with it, and no friction is caused which could 

 interfere with its motion. 



Mr. Conrad Beck exhibited a new portable microscope 

 suggested by Mr. Murray. He said that this instrument had 

 been designed to meet the wishes of Mr. James Murray, the 

 well-known explorer, who was anxious to have a microscope 

 extremely small and portable, and which could be used in the 

 field. Being away from the comforts of civilization, in 

 tropical forests, he would be debarred from the luxury of 

 chairs and tables, and the microscope was therefore so 

 designed that it had one leg. which could be strapped to a 

 walking-stick, which had been driven into the ground, and the 

 observer could sit with the stick projecting from the ground 

 between his legs, and the microscope could be inclined 

 by means of the usual joint to a convenient position. 

 The instrument was on the model of the Star Microscope, 

 with an aluminium stage, and all the superfluous metal 

 removed to make it extra light. It had a sliding coarse- 



adjustment, a micrometer-screw fine-adjustment, and a small 

 substage condenser, with iris diaphragm. It was provided 

 with two loose legs, which screwed into the single leg-base, 

 making it into a tripod for use on a table in the usual way, 

 when such a support was available on the return from an 

 expedition. I'or the study of pond-life on the spot this instru- 

 ment was especially desirable, as the naturalist on the walking- 

 ing-stick-stand principle might spend many profitable hours in 

 pleasant weather in conducting his microscopical examination 

 at the side of the pond, or on the country-side in the open air. 

 Mr. Murray remarked that as the journey he was about to 

 undertake had to be made without the assistance of carriers, 

 it became important to reduce the weight to the utmost, 

 because every ounce put into instruments to be taken must 

 be deducted from the amount of food which could be carried. 

 Therefore, remembering his previous experience with the Star 

 Microscope on his journeys, he asked Mr. Beck if he could 

 improve upon that instrument in the matter of weight. The 

 present microscope was the result. It was true that the 

 necessity for unscrewing the legs of the tripod introduced a 

 structural weakness, but the instrument was intended to be 

 primarily used on a walking stick. Its use in the ordinary 

 way. on a table, was a secondary matter. It was not antici- 

 pated that one would be able, as Mr. Beck had said, to sit 

 comfortably and work with the microscope ; that was usually 

 impossible in the Amazonian forest. It was proposed to have 

 the walking-stick sufficiently long to enable the observer to 

 work standing. Quite possibly the conditions would prevent 

 work, but it was hoped sometimes to rig up a net to keep out 

 insects and allow a little work to be done. Mr. Beck had not 

 stated what the weight of the microscope was. Complete in its 

 case, as fitted for use on the table, it weighed two pounds. 

 But even that was far too much to take on such a journev ; for, 

 as he had said, only so much could be taken, and the heavier 

 the instruments, the less the quantity of food which could be 

 carried. Therefore, when the difficult journey began, the 

 case of the microscope would be left behind, the two supple- 

 mentary legs would be unscrewed, and the microscope folded 

 up and wrapped in a spare shirt. The weight, without the 

 case, was only one pound. 



HOrRVDIi-M GRAXUL.ATVM iL.I— The water at the 

 Welsh Harp reservoir, Hendon, is very low, and it may be of 

 interest to some to know that large stretches of mud are at 

 present — July 20th — in many places covered with the singular 

 little plant Botrydinin grainilatnni. It is not so plentiful 

 as it was last year, vide Journal of the Ouckett Micro- 

 scopical Club, Ser. 2, Vol. XL, No. 68, page 209, probably 

 because, with the drought and great heat, the mud is dried too 

 quickly for the plant to develop. Botrydiiini does not seem 

 \ery common in the London district, but here it covers an 

 immense area. 



J. B. 



ORNITHOLOGY. 



By Hugh Boyh Watt. M.B.O.U. 



DISTRIBL' rioN OF TH1-: NKiHTlNGALE IN 

 GREAT BRITAIN— FIRST OCCURRENCE IN SCOT- 

 L.-\ND. — Connnenting on the note in our last number (page 

 282) a correspondent writes as follows: — "It appears to me 

 that the whole body of evidence collected by Messrs. Ticehnrst 

 and Jourdain wants to be rearranged with respect to its salient 

 features; restated to show the value or valuelessness of its 

 component parts ; and, generally, to be dealt with in as broad, 

 critical, and philosophical a spirit as can be brought to bear 

 upon it. I am pleased that the information has been brought 

 together; more than that I cannot say. unless that I am 

 dissatisfied with the want of any adecjuate examination of it 

 by the authors of the paper." 



Our correspondent (who writes from Scotland) further 

 remarks that the physical difticulty of extension was overcome 

 when the Nightingale had reached the valleys of the Dee, 

 Weaver, and Mersey in Cheshire, and that there was 

 consequently nothing physical to prevent extension into 

 Lancashire ; also that if the species had been in Yorkshire 



