500 



NATURE 



[August 17, 19 16 



other countries in its treatment of the mentally 

 defective class." He points out the ^reat advan- 

 tage of "the physiological education of the 

 senses " (Seguin) of these children, and afterwards 

 of their mental and moral education, both to the 

 individual concerned and to the community. He 

 shows how such children can find occupation and 

 happiness as inmates of permanent working 

 homes and contribute appreciably to the support 

 of such homes, also how the " improved imbecile " 

 is of far less risk to future generations, especially 

 if carefully supervised. 



Certain weak points in the Acts are dealt with, 

 particularly the inadequate provision for " back- 

 ward children," who tend to gravitate to the 

 " special " schools, and the inadequate after-care 

 of the children on leaving the institutions. This 

 latter defect must necessarily damp the enthusi- 

 asm of the teachers, on whose devoted self-sacri- 

 fice the efficient working of the Acts is largely 

 dependent. We strongly recommend the book to 

 all interested in the subject, though mainly written 

 for the medical profession. W. F. B. 



The Microscopy of Vegetable Foods, with Special 

 Reference to the Detection of Adulteration and 

 the Diagnosis of Mixtures. By Drs. Andrew 

 L. Winton, Josef Moeller, and Kate Barber 

 Winton. Pp. xiv + 701. Second edition. 

 (New York : John Wiley and Sons, Inc. ; Lon- 

 don : Chapman 'and Hall, Ltd., 1916.) Price 

 275. 6d. net. 

 Just as the sophistication of foods and drugs has 

 developed, so have the means of detecting them 

 been devised. For this purpose microscopical 

 examination is one of the most important proce- 

 dures, and a knowledge of the microscopic charac- 

 ters of the products and of their chief adulterants 

 is therefore essential. Not only the analyst, but 

 the miller, the brewer, the oil-presser, the cattle- 

 food manufacturer, the canner, and the coffee and 

 spice grinder, should all be conversant not only 

 with the naked-eye characters, but also with the 

 microscopic structure of their raw materials. 



The present book, now in its second edition, 

 deals with the needs of most of these industries, 

 and the authors have, we think, successfully 

 accomplished their task. 



First, equipment, methods, and general prin- 

 ciples are dealt with, after which the microscopic 

 characters of the various products and their chief 

 adulterants and impurities are described. In this 

 way grain, oil-seeds, legumes, nuts, fruit and 

 fruit products, vegetables, alkaloidal products and 

 their substitutes (coffee, tea, cocoa, etc.), spices 

 and condiments and commercial starches, are all 

 considered at length, and an enormous amount of 

 valuable information is collected and collated. 

 The text is illustrated with no fewer than 635 

 figures, and concludes with a full bibliography, 

 glossary, and index. The book is, of course, 

 especially written for American practice, and 

 many articles are described which are rarely met 

 with in this country, but it will be found none the 

 less useful bv our analysts and laboratories. 



R. T. H. 



NO. 2442, VOL. 97] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself 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.] 



A Peculiar Thunderclap. 



Possibly some one of your readers may be able to 

 throw light upon the peculiarity of a thunderclap which 

 occurred here during a severe thunderstorm on July 27. 

 This parish lies in a hollow of the hills, and almost 

 always escapes close contact with thunderclouds. On 

 the date mentioned a peal of extraordinary suddenness 

 resembling the crashing burst ot a big gun followed 

 instantaneously a vivid flash at my point of observa- 

 tion. Two or three trees were afterwards observed to 

 have been struck, and a paling rai] near some wire was 

 split into pieces and thrown some distance. Now the 

 peculiarity is this : that very similar experiences were 

 noted at places more than a mile distant and in various 

 directions. The same crash following immediately on 

 the lightning was noted by quite a number of inde- 

 pendent witnesses. A mile to the east of this dwelling 

 the lightning was seen to run down a wire fixed to 

 the top of a flagstaff. About a mile to the north a 

 farmer driving home was alarmed to see the lightning 

 flash along the wire paling by the roadside and split 

 one post at least and cast the fragments on the road. 



On considering all the circumstances, I think the 

 following may be an explanation. The thunderclouds 

 which contributed mostly to the storm were floating at 

 a pretty high elevation, possibly 2000 ft., as during 

 the greater part of the day they were just grazing the 

 tops of the hills. But about 3 p.m. a bank of cloud 

 began to form in this hollow much nearer the ground, 

 and half an hour later, when the thunderclap came, the 

 light was much obscured. My opinion is that the 

 lower cloud drew an overwhelming charge from the 

 clouds above, and accordingly flashes sped to earth 

 from several points at the same instant. 



I have, of course, made certain that we are dealing 

 here with one and the same thvmderclap, as was not 

 difficult to do, seeing that all the other peals of thunder 

 were comparatively distant. John Don. 



Lumphanan, Aberdeen, July 30. 



The Gun-firing on the Western Front. 



The firing of very heavv guns at a great distance 

 was clearly audible at Harpenden throughout the; 

 days of August 7 and 8, as well as on previous 

 occasions. The direction of the sound is evidently 

 from the south-east, and that of each explosion lasts 

 about two seconds. Our elevation is 440 ft., and th 

 local wind has been from west to north-west. TIi 

 distance between Harpenden and Bapaume would b 

 about 185 miles. Spencer Pickering. 



Mr. Piper's letter (Nature, August 3) is interesdn^ 

 My extended experience confirms his. When th 

 great bombardment began I was staying at a farn 

 house on high ground near Chilham, Kent. We hear 

 the firing day and night during the two weeks, an^ 

 I roughly calculated that three or four guns were fin 

 per second. During almost all the time the wind w- 

 S.W\, and often quite strong, yet this did not interfer' 

 with the sound if one was sheltered from the win'^ 

 and awav from rustling foliage. 



The firing front would be S.E., and about 100 mile 

 away. I. W. Boothroyd. 



9 The Circus, Greenwich, S.E. 



