Feb. 6, 1879] 



NATURE 



3^1 



by the Jews [Levit. xi. 22], and Herodotus mentions a 

 tribe of Ethiopians which fed on locusts, which came in 

 swarms from the southern and unknown districts. 



Mr. Riley speaks of good broth being made " by boiling 

 the unfledged Calopteni for two hours in a proper quantity 

 of water, and seasoned with nothing but pepper and salt ; 

 the broth is hardly to be distinguished from beef broth." 

 Boiled, fried, or roasted the full-grown are said to make 

 pleasant food, and ground and compressed they will keep 

 a long time. The other uses suggested are as fish bait, 

 as manure, and as a source of formic acid. 



There are altogether twenty-seven appendices occupy- 

 ing 279 pages, the last appendix giving the bibliography 

 of the subject. 



GUTHRIE'S PHYSICS 

 Practical Physics, Molecular Physics, and Soufid. By 



Frederick Guthrie, Ph.D.,F.R.SS. L. and E., Professor 



of Physics in the Royal School of Mines, London. 



(London: Longmans, Green, and Co., 1878.) [London 



Science Class-Books, edited by G. Carey Foster, F.RS., 



and Philip Magnus, B.Sc., B.A.] 

 " 'T^HE works comprised in this series," the editors tell 

 J- us, "will all be composed with special reference 

 to their use in school-teaching ; but, at the same time, 

 particular attention will be given to making the informa- 

 tion contained in them trustworthy and accurate, and to 

 presenting it in such a way that it may serve as a basis 

 for more advanced study." 



The little word but, which we hare taken the liberty 

 to emphasise, seems to hint at some opposition between 

 accurate statements and school-teaching, which, if not a 

 fundamental necessity, is at least a universally existing 

 phenomenon in the present order of things. This series 

 of class-books is by no means the first attempt to procure 

 books for children from writers of scientific reputation ; 

 and Prof. Guthrie, the author of this little bonk on prac- 

 tical physics, has himself invented several experimental 

 methods at once interesting, ingenious, and simple. 



If a child has any latent capacity for the study of 

 nature, a visit to a real man of science at work in his 

 laboratory may be the turning-point of his life. He may 

 j not understand a word of what the man of science says 

 to explain his operations, but he sees the operations 

 themselves, and the pains and patience which are 

 I bestowed on them ; and when they fail he sees how the 

 man of science, instead of getting angrj', searches for 

 the cause of the failure among the conditions of the 

 operation. 



Accordingly, in this little book the parts which are 

 most interesting, whether to young or old, are those in 

 which Prof. Guthrie describes his own beautiful experi- 

 ments on the size of drops and bubbles, or teaches us 

 how to blow glass. But if he once opens his ears to the 

 siren song of the scientific imagination, floating down 

 from heights unprofaned by experiment, through the 

 window of the laboratory, and makes three paces through 

 j the room from the blowpipe to the lecture-table, we 

 know that the curse has come upon him, and that for 

 him it will never more be possible to reconcile the claims 

 of accuracy with those of school-teaching. 

 What but some vile enchantment could have induced 



an intelligent man to begin his discourse to the poor little 

 children in this style : — 



" § I. Hardness. Form-elasticity.— The pressure re- 

 quired to alter the relative positions of two contiguous 

 parts of a body measures its hardness. As this pressure 

 is greater with greater surface of contact, some unit of 

 surface must be fixed upon. The term hardness is gene- 

 rally applied loosely to difficulty of fracture. The follow- 

 ing remarks may show that our speech and ideas in 

 regard to hardness are deficient in precision. Glass 

 is said to be harder than lead, yet a glass cup is more 

 easily broken than a leaden one — more easily broken, 

 though not so easily bent. Hard bodies are always 

 elastic ; elastic bodies are not necessarily hard, nor are 

 they necessarily brittle, nor are soft bodies necessarily 

 plastic. Toughness seems to imply a resistance to change 

 of form, which resistance increases more rapidly than the 

 displacement ; thus, while a band of vulcanised caoutchouc 

 will be extended to a degree proportional to the weight 

 hung at one end, a leathern strap will not be extended 

 twice as far if the weight on it is doubled. Toughness is 

 generally associated with texture, and stretching causes 

 partial fibration in the line of pull." 



Here is a teacher who, with all the stores of science to 

 choose from, selects, as the first lesson to a child, the 

 necessity of fixing on a unit of surface, which, however, 

 he makes no attempt to do, but goes on to harangue him 

 on the deficiency in precision of our ideas and language 

 in regard to hardness. 



The poor child is not responsible for this want of pre- 

 cision ; his first duty is not to reform his language, or 

 even to criticise it, but to learn it, and if there is any part 

 of human knowledge about which our speech and ideas 

 have become tolerably precise, let us teach him that first, 

 so that he may have some hope that knowledge is attain- 

 able before we let him see, as we must at last, how con- 

 fused our own notions are. 



Whether a child receives any special instruction in 

 science or not, it is of unspeakable advantage to him if he 

 is not put in the way of explaining things by false hypo- 

 theses. The difficulty which we have in recognising the 

 paradoxical character of some of the most celebrated para- 

 doxes shows how much has been done by the teachers of 

 the last two centuries in causing false principles to be for- 

 gotten. The paradoxes are no longer paradoxical, be- 

 cause the dogmas which made them so are now known 

 only to the owls and the bats. 



We have selected a few statements in this book which 

 we do not remember to have seen before. 



(When a wire is stretched by a weight) " it may be 

 assumed that the volume of the metal remains approxi- 

 mately unchanged, so that if the elongation is such that 

 the length m becomes n, the original diameter d becomes 



vr'*-^>- 



" A drop of water on a board strewed with powdered 

 resin is nearly spherical." " The spherical is the form in 

 which the mean distance of all parts from the centre of 

 mass is the least. It is the most compact form for a given 

 mass. This shows that cohesion moulds the drop to the 

 spherical form " (p. 8). 



Does Prof. Guthrie take his science from Rogers' verses 

 on a tear ? We refer him to Shakespeare (" King John," 

 Act iii. Sc. 4) as a better authority on Capillary Attrac- 

 tion : — 



