424 



NATURE 



[April I, 1875 



mon" ; and the non-applicability to present visitors to 

 the Devil's Dyke, of the remark that " there arc bustards 

 on the wide downs near Brighthelmstone " ; and to those 

 who spend their summer at Eastbourne, that " Cornish 

 choughs abound and breed on Beachy Head, and on all 

 the cliffs of the Sussex coast." A lengthy list of refer, 

 ences is given with regard to the habits of the cuckoo, 

 a subject on which further reliable information is much 

 needed. 



The typography, paper, and binding of the work are all 

 that can be desired, and Bewick's drawings add further to 

 its general interest. 



OUR BOOK SHELF 



Mia-oscopical Notes regarding the Fungi frcsetif in 

 Opium Blight. By D. D. Cunningham, M.15., Surgeon 

 H.M. Indian Medical Service. (Calcutta: Office ot the 

 Superintendent of Government Printing. 1875.) 

 Dr. Cunningham has devoted much care and attention 

 to the study of the fungi present in the opium blight, and 

 the results of his labours are given in the present 

 pamphlet. The most important fungus present, and the 

 one really causing the blight, is a species of Peronospora, 

 and thus belongs to the same genus as our own too well- 

 known potato-disease fungus. As in Indiathe Peronospora 

 affects the opium crop very seriously, it is a matter of the 

 highest importance to have the life-history of such a pest 

 worked out thoroughly by a competent observer. The 

 Pcronosporaarborescens, which in Indiaattacks the 0|5ium 

 poppy, is to be met with in this country on the red poppy 

 {Papavcr Rhccas). Dr. Cunningham invariably found the 

 Peronospora present in blighted leaves, and he describes 

 fully the mycelium and the conidia of the fungus. The 

 mycelium spreads through the intercellular spaces of the 

 leaf, branches coming to the surface through the stomata, 

 which ramify and produce the conidia. The conidia 

 apparently do not produce zoospores. The se.\ual mode of 

 reproduction by antheridia and oogonia was not observed, 

 even although De Bary has already described the oogonia 

 of this fungus. The life-history thus is imperfect, and we 

 must urge Dr. Cunningham to persevere and not rest 

 satisfied until he has observed the whole of the stages of 

 this fungus. 



After the parasite has done its work, the leaves of the 

 poppy become infested with a number of other fungi, 

 chiefly saprophytes, and Dr. Cunningham carefully de- 

 scribes and figures several of the forms. 



W. R. M'Nab 



Logarithmic and Tri'j;ono)nctrical Tables for .Ipproxi- 



matc Calculation. By J.T. Bottomley, M.A., P'.R.S.E. 



(London and Glasgow : Collins and Co., 1S75.) 

 These tables were primarily arranged by Mr. Bottomley 

 for the use of the students of the Natural Philosophy 

 Class in Glasgow University, but we beheve many other 

 students will feel grateful to the author for having pub- 

 lished them. 



An f is> , handy book of tables such as this has been 

 much wanted for Mathematical and Natural Philosophy 

 Classes in the Universities and for advanced schools. 

 There is no reason why, with a really convenient book, 

 boys should not all learn logarithmic arithmetic as soon 

 as they know decimals. But the books hitherto in use are 

 too formidable. Moreover, practical calculators will find 

 much use for four-figure logarithms, sines, &c., and many 

 people who never use logarithms will be able to do so 

 with ease when they have a four-figure table. 



Mr. Bottomley has in this manual arranged (on the 

 plan of De Morgan, we believe, who first applied it to 

 logarithms) sines, tangents, logarithmic sines, and loga- 



rithmic tangents, and has printed them, with the loga- 

 rithms and antilogarithms, each table on two facing paces. 

 We heartily approve of Mr. Bottomley's plan, and 

 recommend his manual to all teachers and students who 

 wish for an easily consulted scientific ready reckoner. 



LETTERS TO THE EDITOR 



[ The Editor does not hold hitnself responsible for opinions expressed 

 by his eorresfoniients. Neither can he undertake to return^ 

 or to correspond with the -writers of, rejected manuscripts. 

 No notice is taken of anonymous co7ninunications,'\ 

 A Gyrostat Problem.* — Answer 



Let /rbe the weight of the fly-wheel. 

 k its radius of gyration, 

 ai its angular velocity in radians per second. 

 W the weight of wheel and case together. 

 a the distance from the centre of inertia to the point of 



attachment of the string. 

 g the force of gravity. 

 The moment of momentum of the wheel round its axis is 

 a lid;". 



The rate of generation of moment of momentum round 3 

 horizontal axis perpendicular to the axis of the wheel, by the 

 couple produced by the action of gravity and the tension of the 

 cord by which the gyrostat is suspended, is equal to the moment 



of llie couple (see Thorn :on and Tail's " Elements of Natural 

 Philosophy," § 236), and is therefore, g 11" a. Therefore the 

 moment of momentum generated in a small time t is g IV a t. 

 Compounding these two moments of momentum by the paral- 

 lelogram of moments, we obtain — 



IV a T 

 IFk" 



where 8 is the angle described in azimuth by the axis of the wheel 

 in the small time t ; and since, when 9 is small, tan S = 6, we 

 have by the question — 



r W a T , 

 \ll-t^ =^" 



tan = ■= 



For Proble: 



: Naturh. vol. 



P- 385- 



