;74 



NA TURE 



[August 8, 1907 



which is represented by a short-winged maritime phase 

 and a long-winged inland form. It is a migratory, two- 

 brooded species, which originally fed upon the native 

 grasses, but has now turned its attention to wheat and 

 other cereals. On reaching a suitable food-supply, the 

 insects congregate on the plants until these are literally 

 covered with individuals of various ages, ranging in colour 

 from the vermilion of the older larvae to the black and 

 white of the adults. When the plant is drained of its 

 juices, the larvje move on to the next one, the adults 

 alone making long migrations. 



The .African honey-guides (Indicatoridie), which have 

 aiquircd parasitic habits parallel to those of cuckoos, are 

 wiser in (iieir generation than the latter, for (as we are 

 told by Mr. A. K. Haagner in the Journal of the South 

 African Ornithologists' Union for June) they are in the 

 habit of breaking the eggs of the birds they select as 

 foster-parents for their offspring. This is illustrated by a 

 plate in the same issue, where two of the fractured eggs 

 are shown. In some cases, however — probably when they 

 are attacked by the future foster-parents — they do not 

 succeed in breaking the rival eggs, in which cvejnt it is 

 probable that the strong hooks on the tip of the beak of 

 the young honey-guides come into play for the purpose of 

 aiding in the ejectment of the other occupants of the nest. 

 A nestling of one species of honey-guide is represented 

 in a second plate. It may be added that most of the 

 plates in this issue are lettered vol. iii., whereas the cover 

 is lettered second series, vol. i.. No. i. The idea of com- 

 mencing a second series with the third volume of this serial 

 thus seems to have been an afterthought — and a bv no 

 means happy one. 



Slugs, according to Mr. B. B. Woodward's presidential 

 address to the Malacological Society for 1907, are more 

 specialised creatures than snails, for among molluscs of 

 all classes there appears to be a general tendency, more 

 especially in the carnivorous types, to discard the shell 

 as the result of the assumption of more active habits than 

 ordinary. Other instances of adaptive modifications in 

 the group are mentioned in the same address. 



I.N Science Progress for July (ii., No. 5), Dr. Bashford 

 discusses the application of experiment to the study of 

 cancer, and summarises the results obtained by a study 

 of the development of transplanted cancer in mice. 



We are asked by the author, Mr. .Arthur Trewby, to 

 state that the little volume entitled "Healthy Boyhood," 

 which was reviewed in our issue of July 25, may be 

 obtained post free for js. 6d. from the author, Fenton 

 House, The Grove, Hampstead Heath, N.W. 



OUR ASTRONOMICAL COLUMN. 



ASTROdRAPIIIC C.AT.\LOC.rE WORK .AT TIIK PeRTH OBSERV- 

 ATORY (W.A.).— Mr. W. Ernest Cooke, Government 

 astronomer of Western .Australia, informs us that the 

 prospects for the astrographic catalogue work are not now 

 so hopeless as they appeared from the report referred to 

 in N.iTURE of May 23 (p. 89). He says that the present 

 Government recognises the importance of the work, and 

 a start has been lately made to measure the plate's. It 

 is feared, however, that the images will deteriorate before 

 the completion of the work. Upon comparing a plate 

 taken a fe\y years ago with a recent one of the same 

 region, the image of a ninth-magnitude star on the foriner 

 was found to be about equal to that of a 95 magnitude 

 on the latter. With reference to the 10,000 standard stars 

 which have to be observed bv means of the transit 

 circle, Mr. Cooke hopes to obtain good positions of all 

 these stars (three observations of each) in ten or twelve 

 years, and certain zones have been completed already. 



NO. 1 97 1, VOL. 76J 



It is proposed to make this list of stars the standard work 

 at the Perth Observatory, observing and re-observing 

 exactly the same list, in order to obtain good determin- 

 ations of the position of each star every ten years or so. 



D.\niel's Comet (i907d). — This comet is now approach- 

 ing the naked-eye stage, and may be found quite readily 

 with small opera glasses. On August 9 it will rise at 

 about i2h. 45m., .some 3I hours before the sun. On 

 .\uCust 14 the comet will be about 46' north of 

 y Geminorum. An observation made on .\ugust i showed 

 no indication of a tail, but the comet has a well-defined 

 nucleus. 



Mars. — ^Telegrams received from the Lowell expedition 

 to the Andes announce that on July 2 Mr. Slipher photo- 

 graphed several of the canals, and that on July 6 canals 

 were seen double and oases were photographed (Astrono- 

 mischc Nachrichtcn. No. 4193, p. 291, July 26). 



In vol. xxvi., No. i (p. i, July), of the Astrophysical 

 Journal, Prof. Newcomb discusses the optical and psycho- 

 logical principles involved in the interpretation of the 

 so-called canals of Mars. From the optical point of view 

 he shows that in the best refracting telescopes the effects 

 of aberration, diffraction, and atmospheric softening will 

 materially increase the breadth of any linear marking. As 

 a rough estimate he submits that a perfectly black line 

 on Mars three miles in breadth might be visible if the 

 surface of the planet were perfectly uniform, but, as it is 

 not, the actual breadth would have to be increased to 

 eight or ten miles in order that the feature might be 

 differentiated from those surrounding it. Aberration, &-c., 

 would spread a marking of this width for some twenty 

 miles on each side, so that the apparent breadth in the 

 telescope would be fifty miles or upward. Allowing this 

 width to each of the 400 canals mapped by Lowell, the 

 total area covered would be 33,000,000 square miles, the 

 actual surface of Mars extending over some 55,000,000 

 square miles. Although this large relative area does not 

 disprove the objective reality of the canal system, it shows 

 how wide the interpretation of the results must of necessity 

 be. when the whole network is crowded on to a disc only 

 20" in diameter. Concerning the interpretation of such 

 features by different observers. Prof. Newcomb gives some 

 illustrated results of a number of interesting experiments 

 he has carried out in this direction. 



Some New Applications of the Spectroheliograph. — 

 Using a temporary spectroheliograph of 30 feet focal 

 length. Prof. Hale has obtained spectroheliograms with 

 the primary slit set on some of the dark lines which are 

 found strengthened in the sun-spot spectrum. The lines 

 employed in this preliminary work were those which 

 appear to be strengthened in the umbra and penumbra 

 and on the photosphere for some distance from the spots, 

 and the resulting photographs show the umbra and 

 penumbra much darker than they appear on plates taken 

 with the light of the continuous spectrum ; the diameter 

 of the spot also appears to be considerably Increased. 

 Lines weakened in sun-spots were also tried and gave 

 definite results, which are, however, less marked than in 

 the case of the strengthened lines. For work with the 

 numerous faint lines of the spot spectrum a large dis- 

 persion is absolutely essential, and a suitable instrument 

 is being constructed for use with the new vertical 

 telescope. 



Prof. Hale has also obtained some spectroheliograms 

 for stereoscopic examination, which, when viewed with a 

 stereoscope, show the masses of flocculi standing boldly 

 above the general level of the hemisphere. A pair of 

 these, taken at an interval of 2h. 5m., are reproduced in 

 the Astrophysical Journal (vol. xxv., p. 314, June). It is 

 hoped that by examining such pairs of spectroheliograms 

 in the stereocomparator changes may be detected in the 

 appearance of the flocculi, &c., which might otherwise 

 escape detection. 



The " .Anxl'ario " of the Rio de Janeiro Observ.atorv. 

 — The twenty-third annual publication of the Rio de 

 Janeiro Observatory, for 1007, which we have just re- 

 ceived, is very ;much like its predecessors, and contains 

 an exposition of various calendars, numerous tables and 

 data useful to astronomers, and a compilation of various 

 physical data which will be found of general use. 



I 



