2 so 



NA 1 URE 



[April 29, 1909 



terrible thing tliat can happen to a Nandi is to dis- 

 please his maternal uncle. Thus it is evident that 

 the Nandi have not long passed from the stage when 

 mother-right obtained. 



Mr. Hollis gives an account, illustrated with good 

 figures, of most of the objects made, worn, or used 

 bv the Nandi, and a number of folk-tales and riddles 





are given in the original language and in translation. 

 It will thus be seen that Mr. Hollis has made a note- 

 worthv contribution to our knowledge of the ethno- 

 logy of British East Africa. A. C. H. 



THE MICROSCOPE IN ENGINEERING. 

 T~\URING the past ten years the young science of 

 -L^ metallography has made rapid strides, and in 

 consequence of this development the microscope is 

 steadily assuming an increasingly important position 

 in the testing-laboratories of those who have to deal 

 with metals, either as manufacturers or users. This 

 position has, however, been accorded to it with some 

 reluctance, partly, perhaps, because at the outset too 

 much was claimed for the instrument. Another cause is 

 to be found in the fact that, as is necessarily the case 

 in all young sciences, theoretical development has out- 

 stripped practical application, and practical men are 

 too apt to regard anything " theoretical " as practi- 

 r-illy useless. But even if we leave aside all questions 

 ?f the promising future applications of these 



NO. 2061, VOL. 80] 



theoretical discoveries, a mass of purely practical 

 results is now available in which the microscope has 

 clearly demonstrated its immediate value. 



Perhaps the most fruitful field for the application 

 of the microscope in the present state of our know- 

 ledge of metals is the study of the nature and causes 

 of breakages or other failures occurring in practice. 

 That the thorough clearing up of such 

 cases, wherever possible, is eminently de- 

 sirable, both in the interests of the 

 parties immediately concerned, and also 

 for the sake of the general advance- 

 ment of our knowledge, is so obvious 

 Ihat it need not be further insisted upon. 

 It is just where our accepted knowledge 

 and our usual practice go wrong that 

 the field for fresh discoveries lies before 

 us. The methods that are available for 

 the posl-mortcni examination of break- 

 ages must depend very much upon the 

 nature of each particular case ; experi- 

 ments that are possible with the broken 

 end of a 12-inch shaft are not applicable 

 to a small brass condenser tube. In 

 every case, however, the first, and per- 

 haps the most vital, step is the exam- 

 ination of the micro-structure of the 

 material close to the actual fracture it- 

 self, and also of the mass of the material 

 lying away from the fracture. The first 

 of these sections will often show whether 

 there is any special local weakness in 

 the metal at the point of actual frac- 

 ture, or whether the fracture itself dis- 

 plays any particular characteristic, for 

 it is well known that the path which a 

 fracture takes among the micro-con- 

 stituents of a metal depends on both the 

 nature of the metal and the inanner in 

 which the fracture was produced. In 

 a given material, for instance, the sec- 

 tion of a tensile or bending fracture is 

 quite different from one produced by 

 sliock or by repeated alternations of 

 stress. The difificulty about these ob- 

 servations lies, however, in preparing an 

 actual section through the fracture, as 

 this is usually either corroded or worn 

 by subsequent friction ; when it is clean 

 ae Lumbwa. aiid fresh, however, the actual fracture 



may be embedded in a thick deposit of 

 electrolytic copper, and a satisfactory 

 section may be cut through the compound mass thus 

 formed. An example of a section of this kind is 

 shown in Fig. i. 



Apart from the examination of the fracture itself, 

 the general micro-structure of the material w^ill, as 

 a rule, reveal whether it has been subjected to any 

 undue treatment during manufacture or use. Thus 

 excessive heating, whether by exposure to an unduly 

 high temperature or to a more moderate tempera- 

 ture for an unduly long time, leaves its trace in the 

 form of a coarse, angular structure which is readily 

 recognised in such materials as steel, brass, _ or 

 bronze. Insufficient rolling or forging, or working 

 at either too high or too low a temperature, can also 

 be readily diagnosed. In many cases a useful guide 

 can be obtained by comparing the micro-structure of 

 the object which has failed with that of a similar 

 object which has given good service ; but this is only 

 necessary where the material in question is one 

 which has not been thoroughly studied, so that the 

 effects of various forms of treatment on the micro- 



