January 20, 1910] 



JVA TURE 



3-1 1 



much discussed in microscopic circles, has Icindlv 

 made a number of rulings of iy40,oooth inch fine- 

 ness, which prehminary experiments indicated as feas- 

 ible for the required purpose, on pohshcd speculum- 

 metal and platinum-iridium, which appear, particu- 

 larly the former, perfectly satisfactory. The fortv- 

 thousandth of an inch being the wave-length of red 

 hydrogen or cadmium light, the distance between two 

 lines ruled at this interval corresponds to only two 

 interference bands. With the i/iath inch dry objec- 

 tives the lines, moreover, are as cleanly cut as spider- 

 lines, and the thickness of a line is less than half a 

 wave-length. Five such lines are ruled in succession, 

 the central one being considered as ihe defining line. 

 A strong finder-line is ruled on each side of the five, 

 and two other strong ones at right angles in order to 

 localise a central part of such a system. It appears 

 perfectly feasible to c^jcry out a stepping-off process for 

 the counting of the total number of wave-lengths of 

 cadmium red light in the British yard, in which such 

 rulings would take the place of the glass plates of the 

 .Michelson or Fabry and Perot etalons, a base line of 

 the thirty-second part of an inch being first 

 actually counted in bands with the aid of the inter- 

 ferometer, between limits defined by two such 

 systems of rulings. The final fraction of every 

 stage in such a process could be absolutely 

 checked by the interferometer in all cases where 

 Michelson found it possible to do so, that is, so far 

 as interference bands are still visible, about four 

 inches; and, as it has already been proved that the 

 accuracy with the rulings is almost as great as with 

 interference bands, this checking ceases to be as 

 imperative as when only the coarse existing defining 

 lines are available. Hence, the future before these 

 rulings appears likely to be both interesting and 

 important. A. E. H. Tutton. 



SOME NEW NATURE BOOKS.^ 

 (i) T N this series of pleasantly written essays Mr. 

 *■ Larken gives an account of some of those 

 features of English (and .Scotch) country districts 

 which usually appeal to nature-lovers. The author's 

 habit of passing lightly from one topic to another but 

 distantly connected with it produces a certain dis- 

 jointedness of style and some needless repetitions, 

 but, taken as a whole, his book is quite good to read, 

 and his knack of interesting one in a disputed point 

 and then abruptly leaving it unsettled is well cal- 

 culated to stimulate personal observation on the part 

 of his readers. 



When attempting to draw conclusions himself, how- 

 ever, he is less happy, being prone to derive the in- 

 herited instincts and habits of an animal directly 

 from the experience of its ancestors. Moreover, one 

 has rather frequent cause to doubt the accuracy of his 

 statements; for example, anyone familiar with the 

 CaligidcB, and the tightness with which they can ad- 

 here, either in or out of the water, even to the smooth 

 sides of a glass dish, will certainly question the re- 

 mark on p. 2ig that a salmon "leaps . . . into the 

 ,ur for the purpose of getting rid of the sea-lice which 

 are attached to him." That "the Brimstone is a 

 genuine child of spring " in contrast with the hiber- 

 nating Vanessid butterflies (p. 244) is contrary to the 

 experience of other entomologists; and " Humming- 

 Birds of New Guinea " (p. iq2) should presumably 



1 (:) "Leisure Hours with Nature" Bv E. P. Larken. Pp. xv+=63. 

 (London : T. Fisher Unwin. iqoo.) Price 51. 



(2) "The Wood I Know •;'" The Me.idow I Know"; "The Stream I 

 Know"; The Common I Know." Edited by W. P. Westell and H. E. 

 Turner. Pp 77 each. (London : J. M. Dent and Co, rgog.) Price grf. 



(3) "The Ruskin Nature Reader." Intermediate Book. Selected and 

 edited by C.. R. Bennett. Pp. x+i8o. (London : I. M. Dent and Co., n.d.) 



Pric 



. 6rf. 



NO. 2099, VOL. 82] 



read " Sun Birds of New Guinea," for humming-birds 

 are confined to western America and its islands. 



The book is illustrated with a profusion of excellent 

 plates, chiefly from photographs. As the greater part 

 of it is concerned with ornithological matters, it is not 

 surprising to find that the majority of the illustrations 

 are of birds' nests. The plate of the comma butter- 

 fly, which we reproduce, is one of a short series of 

 admirable insect studies. 



(2) These four little volumes will be useful to those 

 who wish to interest children in natural history. 

 They treat of the varied aspects of their several sub- 

 jects in a clear and interesting manner, and are well 

 illustrated by plates (both coloured and from photo- 

 graphs) and by figures in the text. One hesitates to 

 criticise such admirable books at such a low price, 

 but the value of some of the plates would certainly be 

 increased if they could be brought more closely into- 

 connection with the chapters which they illustrate; 

 and where this is impossible reference should be made 

 to them in the text. Some statement of the scale of 



many of the figures would make these much more 

 useful; in chapter ix. of "The Common I Know," 

 where this is particularly needed, it could easily be 

 made by the insertion beside each figure of a line 

 indicating the length of the living specimen. On 

 p. 30 of the same volume the association of 

 two figures of plants drawn to different scales 

 is apt to mislead. But even as they stand we 

 are far from wishing to condemn the figures. Apart 

 from size, they show clearly the salient characters 

 of the objects described ; the reproduction of the photo- 

 graphs has been beautifully executed, and the coloured 

 plates are wonderful at the price. We can thoroughly 

 recommend the books for (elementary) school use. 



(3) This " collection of literary extracts to accom- 

 pany a course of nature-study " includes prose and 

 poetry, with a variety of subjects ranging from 

 Ruskin's " Plants " and Thoreau's " Brute Neigh- 

 bours " to fairy stories such as " The King of the 

 Vipers" and Ruskin's "Visit from the South-West 

 Wind." Several of the extracts are old favourites 



