May 23, 1918] 



NATURE 



223 



of maximum pressure. This must lead to con- 

 siderable labour when finding- the best relation 

 between the capacities of chamber and bore for 

 a new type of gun. 



Other additions to Col. Lissak's text are : de- 

 scriptions of the manufacture of the American 

 nitrocellulose powder ; the modern hydro-pneu- 

 matic recoil systems; the 12-in. mortar carriage, 

 model 1908; and the Lewis air-cooled machine- 

 gun. Otherwise Col. Lissak's text has been 

 largely adhered to, but the subjects have been 

 rearranged in a more logical sequence. 



The chapter on interior ballistics is marred by 

 the number of errors in the formulae which have 

 ( scaped notice. 



OUR BOOKSHELF. 



J'lquipment for the Farm and the Farmstead. By 

 Prof. H. C. Ramsower. Pp. xii + 523. (Boston, 

 Mass.; London, etc.: Ginn and Co., 1917.) 

 Price I05. 6d. net. 

 Ix this volume Prof. Ramsower has broken new 

 ground and given us an account of the equipment 

 necessary for starting and maintaining a farm in 

 the United States, with special reference to the 

 conditions in the Middle West. About half of the 

 book deals with the construction of the farmhouse 

 and buildings, and the other half with farm im- 

 plements. As material for construction about the 

 farm, Prof. Ramsower recognises the great advan- 

 tage of concrete, though he also realises its disad- 

 vantages. There is ain interesting chapter on the 

 lighting of the farmhouse. Water supply and sew- 

 age are also dealt with at length, and considerable 

 stress is laid on the need for adequate sanitation. 

 The remainder of the book deals with farm im- 

 plements. The plough comes first as the basal 

 tillage tool, "walking" ploughs and "sulky" 

 ploughs being both described. The former is the 

 type commonly seen in this country when the 

 ploughman has to walk; the "sulky" plough, on 

 the other hand, allows him to ride; it takes its 

 name from the light two-wheeled carriage used in 

 America, and is called a " sulky " because it accom- 

 modates only one. The difference between them 

 lies in the amount of friction ; the ordinary plough 

 rests on a smooth slade or sole, which slips over 

 the ground; the "sulky" plough, on the other 

 hand, rests on wheels. Thus, the sliding friction 

 of the ordinary plough is replaced by rolling fric- 

 tion, and, in consequence, it is possible to add the 

 weight of the frame and the driver without materi- 

 ally, damaging the draft of the plough. 



Harrows are dealt with at length : the spike- 

 tooth forms, as commonly seen here, and the 

 spring-tine and the disc forms, which seem to 

 have great possibilities. There is also a useful 

 chapter on the gasolene and oil engine, in which 

 file author describes not only the engines them- 

 selves, but also sorhe of the many troubles which 

 arise directly an engine or tractor is set to work 

 on a farm. 



The book is w'ell illustrated, and will be found 

 very helpful to serious farm students. 

 NO. 2534, VOL. lOl] 



Everyday Physics: A Laboratory Manual. By 



J. C. Packard. Pp. vi+136. (Boston, Mass.; 



London, etc. : Ginn and Co., 1917.) Price 



45. 5d. net. 

 A LABORATORY manual outlining a course in physics 

 " adapted equally well to jireparation for college 

 and to the immediate requirements of everyday 

 life " may be regarded as a sign of the times. It 

 is becoming recognised in an increasing degree that 

 the fundamental principles of physical science must 

 be employed not only in the laboratory, but also in 

 the home and in the factory. Mr. Packard, who is 

 science master at the High School, Brookline, 

 Massachusetts, has produced a volume of consider- 

 able interest and originality, which may be recom- 

 mended to teachers who are planning a practical 

 course in science for a secondary school. More 

 than sixty exercises are given, covering a wide 

 range of subjects, the usual experiments in a 

 physics course being combined with newer exer- 

 cises involving the use of commercial apparatus. 

 Thus we have noFonly a " Study of a Metric Rule," 

 but also a " Study of a Water Meter," with instruc- 

 tions for testing the accuracy of the meter by 

 filling a tank of w^hich the dimensions are to be 

 determined. This is followed by exercises on gas 

 and electricity meters with clearly drawn diagrams 

 for each case. 



A few of the more novel subjects studied include 

 a water motor, a life preserver (illustrating the 

 principle of Archimedes), an anemometer, a gas or 

 alcohol stove, methods of domestic heating, light- 

 ing, and ventilation, the mechanism and action of 

 a clock and of a sewing machine. Nearly every 

 exercise is preceded by an introduction, intended 

 to show the bearing of the topic in hand upon re- 

 lated subjects, and is followed by questions or 

 problems emphasising the immediate application of 

 the principle involved to the affairs of daily life. 

 Topics for further study and investigation are sug- 

 gested, and the author points out that much valu- 

 able material for every department of science can 

 be gathered from trade catalogues. The student 

 is instructed as to the best method of recording 

 the results of his observations, but, as the author 

 rightly says, the object of a laboratory course in 

 physics is not to make a note-book, but to teach 

 the principles of physics and to emphasise their 

 practical application. H. S. A. 



LETTERS TO THE EDITOR. 

 [The Editor does not hold hitnself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



The Supposed "Fascination" of Birds by Snakes. 



I HAVE now received a reply from Capt. G. D. H. 

 Carpenter to my letter sufjgesting that he had ob- 

 served an instance of "mobbing." It was written in 

 January last from Lulanguru, seventeen miles east of 

 Tabora, in ex-German East .Africa : — 



"Regarding my snake and bird ob'^ervation, the 

 l)irds' behaviour was quite unmiNiwl^.iMc ; they were 



