April 22, 1875] 



NATURE 



483 



generalities and assumptions found in" the general run of 

 physical treatises, so that the student is left in the lurch 

 just at the critical moment when he most needs help. It 

 is quite refreshing to notice the minute care with which 

 Prof. Weinhold describes the construction of each piece 

 of apparatus. As illustrations of this take the instructions 

 for cutting glass on p. 14, for soldering on pp. 27 and 28, 

 for cutting screws on pp. 93 and 94 ; and especially valu- 

 able are the directions for making various simple forms 

 of binding screws given on pp. 656-660. Every woodcut 



is drawn to scale, every bit of apparatus employed has its 

 dimensions given, every difficulty is pointed out, and 

 failure thus made almost impossible. 



Nor is this work only useful for science students. We 

 venture to sayany intelligent boy of twelve to fourteen years 

 old might begin this book by himself, and, steadily work- 

 ing at it out of school hours and during the vacation, 

 would in twelve months' time have not only mastered its 

 contents, but have made for himself a very respectable and 

 thoroughly useful collection of physical apparatus, the 



Fig. I. — Experiments in liquid films. 



history and meaning of every fragment of which will be 

 known and loved as part of his nature. 



But we shall be doing Prof. Weinhold more justice if 

 we give our readers a few e.xtracts from his hand-book. 

 Here, for example, is a simple and elegant method of 

 demonstrating the tension of liquid films. A ring is 

 dipped in soap solution contained in a flat saucer, and 

 then withdrav.'n ; a film is thus formed after the manner 

 of Plateau's e.xperiments : — "If a very fine silk thread, 



Fig. 2. — Weights raised by liquid pressure. 



wound from a cocoon, is tied to two points of the ring a 

 and b (Fig. r, a, b), and the film which is formed be 

 broken within the portion c, by the finger or a rolled 

 piece of blotting-paper, the unbroken portion of the film 

 will contract and stretch the thread into a beautiful cuive. 

 If the thread be fixed only at a and held by the finger at 

 b, its length may be altered at will, but the contraction of 



the film will always stretch it so as to form an arc of a 

 circle. If a small loop is made at the end of the thread, 

 (Fig. I, c, d), the latter fixed at a, and the film broken at 

 b, the thread of the loop will form a complete circle 

 within the ring." 



In speaking of hydrostatic pressure, the following 

 simple arrangement is described : — " A pig's bladder, or, 

 better still, that of an ox, is cut down near its mouth so 

 far that the end of a glass tube of about the thickness of 

 a finger, and ten centimetres in length, may be passed 

 through the aperture and firmly tied (if necessary with 

 the help of a cork). A longer glass tube is connected 

 with the shorter by a piece of tight-fitting indiarubber 

 tube, and jheld in a vertical position by the fork of the 

 retort stand. The bladder is moistened, placed upon the 

 table, flattened out as much as possible, and a piece of 

 board, such as the lid of a box or a drawing-board, laid 

 upon it, so that the bladder is not in the middle, but close 

 to the edge of the board. At each end of the bladder 

 small blocks of wood about two or three centimetres high 

 are placed, in order to protect the glass tube, which 

 reaches under the board, from being broken by the pres- 

 sure of the board and the weights to be afterwards placed 

 upon it. By potiring water from a bottle or through a 

 funnel into the tube, the bladder is filled until the board 

 begins to rise above the blocks and is in contact with the 

 table only along one edge." 



There is a neat illustration of the work done by falling 

 bodies on p. 74, but the author is evidently unacquainted 

 with Prof. Ball's admirable manual on experimental 

 mechanics, wherein the student will find mechanical 

 problems more rigidly and amply put to the test of 

 experiment. 



The section on Sound, we observe, omits all reference 

 to the beautiful demonstrations which can be given of the 

 reflection and refraction of sound, nor is there a single 

 reference to the subject of sensitive flames, the value of 

 which as phonoscopes should, in our opinion, hardly have 

 been overlooked. The following simple method of making 

 Kcenig's gas-flame manometer is given on p. 395. For 



