4i8 



NA rURE 



[February 28, 1901 



way, so that the financial position can be readily under- 

 stood. A pupil who has been taught arithmetic in a 

 reasonable way can adapt his knowledge to the forms 

 of bookkeeping in a few weeks when placed in an office. 

 For people who have not had the advantage of a rational 

 education, it is necessary to draw up hard and fast rules, 

 which must be obeyed in order to keep accounts in- 

 telligibly. The volume under notice does this, by show- 

 ing as simply as possible how a trader unfamiliar with 

 bookkeeping may construct, keep and balance a set of 

 account books suited to his own business. A set of 

 " Automatic Balancing Charts" is published separately 

 as a supplement to the book, and they are drawn up in 

 such a way that it is almost impossible for a person of 

 average intelligence to make an incorrect entry upon 

 them. Both the book and the charts should prove of 

 service to business men unfamiliar with the intricacies 

 of bookkeeping. 



Reports from the Liboratory of the Royal Colles^e o/ 

 Physicians, Edinbur^s^h. Edited by Sir Batty Tiike, 

 M.D., and D. Noel I'aton, M.D, Vol. vii. (Edinburgh : 

 Oliver and Boyd, 1900.) 

 This volume consists of a series of original papers 

 which, since the end of 1897, have emanated from the 

 laboratory of the Royal College of Physicians of Edin- 

 burgh. Practically all these papers have been published 

 previously in the medical or scientific journals, and in 

 this form have no doubt been read by those interested in 

 their subject-matter. This is, however, perhaps only 

 partially true of two reports which were presented re- 

 spectively to the Fishery Board for Scotland and to the 

 Prison Commission for Scotland. The first report con- 

 sists of sixteen monographs on the life-history and the 

 physiology, under varying conditions, of the salmon ; 

 and concludes with a monograph, by Dr. Dunlop, upon 

 the food value of the salmon at different seasons, and 

 obtained from different sources. 



Dr. Dunlop is also the author of a report to the Prison 

 Commission for Scotland upon prision dietaries. The 

 report seems to be an exhaustive one, and contains many 

 suggestions with regard to the adaptation of the diets 

 in prisons to the varying conditions and labour employ- 

 ments of the prisoners. 



Mother, Baby and Nursery. By Genevieve Tucker, 

 M.D. Pp. xvi + 193. (London: T. Fisher Unwin, 

 1900.) Price IS. 

 This is one of the many manuals written for the guid- 

 ance of joung mothers. The writer is an American 

 doctor, but suitable to every mother are the clear and 

 practical directions on the management of herself and 

 her infant. The earlier cliapters are concerned with 

 heredity and the conditions favourable for the unborn 

 child. The practical advice is valuable, but it is mis- 

 leading that the author's opinions on questions of 

 heredity are stated as generally acknowledged facts. The 

 chapters on the care of the infant are suggestive and 

 helpful, and the importance of early training m good 

 habits beginning during the first month of life is insisted 

 upon duly and wisely ; but the following advice is extra- 

 ordinary and not to be recommended : " Take a good- 

 sized raisin, cut open, taking out the seeds, put it on the 

 umbihcus." A chapter containing a classification of the 

 diatheses of infants (scrofulous, tuberculous types, &c.) 

 seems out of place in a manual of this description. At 

 the end of the book there is a short and emphatic 

 summary of what is and what is not to be done in the 

 nursery ; but among the '' nursery don'ts " we notice the 

 omission of a warning against a practice too common, 

 at any rate, in this country, namely, the use of so-called 

 baby soothers. 



Interest is added to the book by the introduction of 

 photographs of young children, but we dislike to see 

 advertisements embodied in the text. 



NO. 163 s. VOL. 63] 



LETTERS TO THE EDITOR. 

 {The Editor does not hold himself responsible for opinions ex- 

 pressed 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. ^ 



Vortex Rings. 



In the course of some experiments preparatory to a lecture 

 on vortex rings, I have introduced certain modifications which 

 may be of interest to teachers and students of science. 

 • The classic vortex-box is too well known to require much 

 description. Our apparatus, which is rather larger than those 

 in common use, is a pine box measuring about a metre each 

 way, with a circular hole 25 cms. in diameter in one end. Two 

 pieces of heavy rubber tubing are stretched diagonally across 

 the opposite or open end, which is then covered with black 

 enamel cloth tacked on rather loosely. The object of the 

 rubber chords is to give the recoil necessary after the expulsion 

 of a ring to prepare the box for a second discharge. Such a 

 box will project air vortices of great power, the slap of the 

 ring against the brick wall of the lecture hall being distinctly 

 audible, resembling the sound of a flip with a towel. An 

 audience can be given a vivid idea of the quasi-rigidity of a 

 fluid in rotation by projecting these invisitile rings in rapid 

 succession into the auditorium, the impact of the ring on the 

 face reminding one of a blow with a compact tuft of cotton. 



For rendeiing the rings visible I have found that by far the 

 best results can be obtained by conducting ammonia and hydro- 

 chloric acid gases into the box through rubber lubes leading to 

 two flasks in which NH4OH and HCI are boiling. Photo- 

 graphs of large rings made in this way are reproduced in Fig. i, 

 the side view being particularly interesting, showing the comet- 

 like tail formed by the stripping off of the outer portions of the 



Fig. I. 



ring by atmospheric friction as it moves forward. It is needless 

 to say that the experiment with the visible rings should be left 

 until the end of the lecture. The power of the air-rings can be 

 shown by directing them against a flat pasteboard box, stood on 

 end at some distance from the vortex apparatus, the box 

 being at once overturned or even driven off on to the floor. 

 A large cluster of burning gas jets can be extinguished by the 

 impact of a ring, a modification of which experiment can be 

 shown on a small scale by shooting a capped shell in a shot-gun 

 at a candle several paces off. If one's aim is good the candle 

 will be extinguished by the invisible vortex. 



For showing the elasticity of the rings by bouncing one off 

 the other, I find that the best plan is to drive two in rapid 

 succession from the box, the second being projected with a 

 slightly greater velocity than the first, all experiments that I 

 have made with twin boxes having yielded unsatisfactory 

 results. 



Though the large vortices obtained with an apparatus of this 

 description are most suitable for lecture purposes, I find that 

 much more beautiful and symmetrical rings can be made with 

 tobacco smoke blown from a paper or glass tube about 2 '5 cms. 

 in diameter. It is necessary to practice a little to learn just the 

 nature and strength of the most suitable puff. Rings blown in 

 this way in still air near a lamp or in full sunlight, when viewed 

 laterally, show the spiral stream lines in a most beautiful 

 manner. I have succeeded in photographing one of these rings 

 in the following way. An instantaneous drop shutter was fitted 

 to the door ot a dark room, and an arc-lamp focussed on its 

 aperture by means of a large concave mirror. The shutter was 

 a simple affair, merely an aluminium slide operated with an 

 elastic band, giving an exposure of 1/300 of a second. A photo- 



