53« 



NATURE 



[October 6, 1^92 



and lower story with the red windows. From this result 

 by a simple step the coloured bands seen when white 

 light is employed are readily explained. Of course, and 

 wisely so, no attempt is made to explain why with mono- 

 chromatic light the windows are seen at all. In the same 

 manner most of the phenomena described or which can 

 be observed by following the clear and simple directions are 

 stated to be what they are, rather than proved or explained. 

 The authoress, guided by her own experience as a school- 

 mistress, is probably right in continually pointing out 

 fresh phenomena of interest, which may or may not be 

 immediately forgotten, rather than in wearying the child 

 with difficult arguments which could at best be imper- 

 fectly understood, and which would be sure in many 

 cases to awaken a feeling of disgust. In short. Sunshine 

 is a kindergarten and not a school. 



Simple and homely language is employed with the 

 greatest propriety, but occasionally it tends to be vague 

 or even to produce a wrong impression. One or two 

 actual mistakes may be referred to in order that they may 

 be corrected in a future edition. 



Thus, it is stated that as a rainbow entirely vanishes 

 when the sun is as much as 42^ above the horizon, we can 

 never see one at noon. " In the summer " should ob- 

 viously be added. The reader is told to spin a top 

 carrying a disk painted half yellow and half blue and he 

 will see green. There is a confusion here between the 

 colour obtained by adding two colours as by spinning, 

 and that which is the result of mixing pigments. As is 

 well known, green is not produced under these circum- 

 stances, but white or nearly white. The four chapters on 

 soap bubbles, which contain much that is sure to please, 

 are supplemented by some special instructions, which, 

 however, are nol quite correct. Fig. 167 is an illustration 

 of an experiment purporting to measure the surface- 

 tension of a soap bubble by the depression of the water 

 level in a quill tube dipping into a glass of water. As 

 the bubble is drawn much larger than the two hands, the 

 pressure within it would not produce any depression of 

 the water below the general level. It would not even 

 visibly affect the capillary elevation. Then it is stated 

 that the surface-tension of pure water is 16-62 grains per 

 square inch. It is, as a fact, a little over three grains per 

 linear inch. The confusion becomes greater in the j 

 passage, "We know exactly how much energy it (the j 

 elastic film of water) has— 16-62 grains per square inch. \ 

 A tube of i-inch bore will lift up 1662 grains of water." j 

 There is one serious fault in the book. Serious because i 

 an experiment is described as though it were being per- | 

 formed to an audience which is not only impracticable 

 and impossible, but which would require in a soap-film a 

 property different in kind to that which it possesses. A 

 school-slate frame with one end removed is hung up so 

 that the remaining end is uppermost. A knitting-needle 

 is cut of such a length that it will slide freely in the 

 groove made to hold the slate. From the knitting-needle 

 a pill-box is hung by threads. The object is to weigh a 

 letter. A soap-film is spread over the frame as far as the 

 knitting-needle. 



'' See how the film is stretching, the knitting-needle is 

 brmgmg it down like a blind. Now we place a letter in 



NO. 1 197, VOL. 46] 



the balance. I know that it weighs just half an ounce, 

 so I can mark on the slate-frame with my blue pencil the 

 place where the knitting-needle stops for half an ounce. 

 I see I was not mistaken in what would take your fancy X 

 I will hang it up here. You shall make one for your- 

 selves, and spend what time you please with it. You 

 will not then easily forget how elastic the film is." 



j Now the surface tension of a soap film is so small that 

 j if the knitting-needle and pill box weighed nothing the 

 I slate frame chosen must have been eight or nine feet 

 j across, and the knitting-needle the same length ; or if 

 the letter and the pill box weighed nothing the knitting 

 needle, if of steel, must have been a great deal finer 

 than any in ordinary use. But even if the experi- 

 ment were being performed on a minor planet, instead 

 ! of at Manchester, where with diminished gravitation 

 j the half-ounce knitting-needle and pill box would only 

 just be sufficient to balance the tension of the soap film, 

 i the description would give the false impression that 

 like a metal or other spring the tension of the soap 

 film increases as the film is stretched, and so is able to 

 rest steadily at some point which depends on the stretch- 

 ing weight. One obviously invented experiment described 

 with all the circumstance and detail that this is, is 

 sufficient to shake one's faith in the genuineness of other 

 demonstrations. C. V. B. 



STRETTON ON THE LOCOMOTIVE. 



The Locomotive Engine and its Development. By 

 Clement E. Stretton, C.E, (London: Crosby Lock- 

 wood and Son, 1892,) 



'"PHE author of this work is well known to the rail- 

 -»- way world as one who has long taken a great 

 interest in everything pertaining thereto. No one 

 probably has a better knowledge of the history 

 and development of the locomotive. It is with 

 much pleasure we welcome the volume before us. The 

 author very properly gives to Trevithick the name of 

 " Father of the Locomotive," he having used high-pres- 

 sure steam, the smooth rail, and the blast pipe, some 

 years before either Hedley or Stephenson began to ex- 

 periment. It is a pity so many men connected with the 

 early progress of the locomotive should have been lost to 

 fame ; all did their share — the few only have been 

 handed down to posterity. William James, for instance, 

 certainly should not be forgotten, he having had a large 

 share of the work in proving the locomotive to be a suit- 

 able machine for hauling trains, as against the system of 

 fixed engines and rope haulage, and to him is largely 

 due Stephenson's success on the Liverpool and Man- 

 chester Railway. 



Richard Trevithick was born April 13, 1771, in the 

 parish of Illogan in Cornwall. He was a mechanical 

 genius in many ways. His first engine was made in the 

 year 1803. This engine ran on four wheels, the boiler 

 was arranged horizontally and had a wrought iron return 

 fire-tube ; the cylinder was 8^ inches in diameter, and 

 the piston had a stroke of 4 feet 6 inches. It was ar- 

 ranged horizontally, the crosshead driving a shaft in front 

 of the boiler by means of a return connecting-rod. This 



