2oG 



KNOWLEDGE. 



[November 1, 1895. 



as to produce the same results each time. I am aware of 

 only one of these. Would some of your readers also state 

 the principle on which they are so arranged? 



Brighton. I- G. Ouseley. 



TASMAXIAX IXSEC'I PESK. 

 To the Editor of Knowledge. 



Sib, — In the copy of Knowledge of February 1st, Lsfij, 

 which has just reached my hands, I notice a series of 

 mis-statements which it may be well to correct. I refer 

 to the notice on page 40, beginning with the words : — 

 "The last Australian mails, etc., etc." I am quite at a 

 loss to account for the information reaching you in the 

 form it has, but it is certainly well to place the matter 

 correctly before your readers. It is true that I, as 

 Government Entomologist, did report on the devastations 

 of the various grass-devouring insects, but Mr. Bos, who 

 is in no way associated with the Government service, 

 controverted my statements, and some of his remarks, no 

 doubt, found their way into the press. In all the Colonies 

 we suffer a tremendous yearly loss from these grass-pests, 

 and I accordingly have been endeavouring to work out 

 their history and discover some possible remedy. The two 

 underground pests from which we suffer the worst are a 

 variety of cutworm, and the larva of a chafer {Ladi- 

 nostenui .') The former emerge from the eggs deposited 

 by the moths about the end of January (answering to 

 July in the N. hemisphere), and commence their work of 

 destruction by feeding on the tender blades and shoots of 

 glasses, which they frequently drag into the holes made 

 by them, and which vary from sis to eight or nine inches 

 in depth, and devour them at their leisure. At the 

 approach of winter they remain in a more or less dormant 

 state, and do not resume their destructive work till the 

 approach of spring. They then gradually mature, change 

 into the chrysalis stage, and alter a few weeks emerge as 

 the perfect moth. The beetle-grub, on the other hand, is 

 three years in the ground, and is more or less active during 

 its whole life, excepting during severe snaps of cold or 

 frosty weather. As the perfect beetle it emerges in our 

 midsummer and commits a certain amount of damage to 

 the foliage of fruit trees. We have another pest which is 

 also most destructive, and which is closely analogous to 

 the migrating " army-worm " of American entomologists. 

 It is the larva of a moth Lcuranium, and as the females 

 can deposit from seven hundred to eight hundred eggs, it 

 is not surprising to find it increasing, under favourable 

 conditions, to an alarming extent. In some years the 

 country is cleared by it. It marches steadily on in vast 

 myriads, and sweeps everything before it. I have heard 

 of the trains being stopped on account of the thousands 

 crushed on the rails rendering them too slippery for the 

 wheels to take grip. I have known of one farmer destrojing 

 two tons of them in one paddock by means of trenches 

 and holes, and I have also seen the creeks filled by them 

 two or three feet high in places. Mr. Box's description 

 of the habits of the cutworm are fairly exact, but that 

 gentleman holds that they feed all through the winter, but 

 this, I feel sure, is not invariably the case. All sorts of 

 remedies have been tried and suggested, but without avail. 

 Where irrigation can be carried on, immense numbers of 

 the caterpillars can be destroyed, but this is not always 

 possible. As the result of careful observations I am 

 myself inclined to the opinion that the only method by 

 winch we can hope to exterminate these imderground pests 

 is by top-dressing with potash salts, and I beheve that in 

 kainit we have the best form in which to apply them. 

 Indeed, I am in every way hopeful that we shall be able 



to check many other pests, such as the scale-insects, 

 aphides, etc., by the use of kainit. I have succeeded in 

 the case of the peach aphis (Aphis pcrsictB nifjer Smith) and 

 I therefore feel very hopeful about others of the same class 

 of insects as well as the pear-slug (Lelamhia cernsi), all of 

 which are dependent upon the sap or green tissues of the 

 leaves. Ei,^T,_ H. Thompson, 



Franklin, Huou, Tasmania Government Fniomolo^iit. 



(Entomologist's Branch). 



[The note in the February number of Knowledge referred to bv 

 Mr. Tliompson, was talien from a Tasmanian paper, and sent to us by 

 a reliable correspondent. — Ed.] 



►-♦-< 



co^•CE^TRIC kainbowp. 



To the Editor of Knowledge. 



Sir. — With regard to the appearance of supernumerary 

 rainbows, referred to in your Correspondence columns in 

 the October number, the explanation of these is given by the 

 wave theory of light, and depends on the theory of inter- 

 ference, combined with that of diffraction. An explanation, 

 based on the interference of hght, was first proposed by 

 Young in 180-1, and was worked out for the first time by 

 Mr. Potter, who published an account of his work in the 

 Cambridge Philosophical Transactions. The final and 

 complete theory was given by Sir George Airy. The 

 problem is a complicated one, and the theoretical con- 

 clusions have been esperimentally confirmed by Prof. 

 Miller, of Cambridge, who caused a pencil of sunlight to 

 pass in a horizontal direction through a narrow vertical 

 slit and fall upon a thin vertical jet of water. When the 

 stream was observed, portions of the primary and secondary 

 bows and a large number of the supernumerary bows were 

 seen forming a set of vertical coloured fringes arranged 

 side by side. The angular radii of the bows when 

 measured agreed with the value indicated by theory. An 

 account of Airy's theoretical investigation will be found in 

 Preston's " Theory of Light." 



I have myself seen on three occasions within a fortnight, 

 while in Strathspey, Inverness-shire, brilliant rainbows 

 with three or four supernumerary bows remarkably well- 

 defined on a very dark background of cloud. 



J. J, Stew.\et. 



7, Mountview Koad, Crouch Hill, N. 



Kotias of JJoofts. 



Major James Bennell and the Bise of Modern English 

 (rcor/raphy. By Clements E. Markham, C.B., F.E.S. 

 (Cassell and Co.) Dalton, Liebig, Faraday, Clerk Maxwell, 

 the Herschels, Lyell, Davy, Pasteur, Darwin, and Helmholtz 

 are familiar names in scientific literature ; but the same 

 cannot, we fear, be said of that of Major Rennell, not- 

 withstanding Mr. Markham's assertion that " he was 

 undoubtedly the first great English geographer." Mr. 

 Markham has certainly done his best to prove Rennell's 

 right to that position, but even if it be granted, we venture 

 to doubt whether Eeunell's work was sutficiently original 

 and striking to interest the public for whom the Century 

 Science Series is intended. Eennell was born in 1712 

 and died in 1830. He is more remembered for his 

 literary labours than for his work in the field, although, as 

 a matter of fact, Eennell carried out a large amoimt of real 

 geographical work. His map of Ilindostau, and the memoir 

 on the geography of India, which accompanied it, earned him 

 the Copley medal of the Eoyal Society, and established his 

 position as a working geographer as well as a man of 

 letters. He surveyed and mapped the many ramifications 



