NATURE 



[May 5, 1887 



For example, the whole range of hypothetical and abstract 

 assertions would require to undergo some preliminary 

 torture : wherever a sentence intends to assert that one 

 fact conditions another, without expressing an opinion as 

 to the actual fulfilment of the condition, we should have 

 to contraposit the sentence and restrict it to the negative 

 form. Thus " policemen seven feet high would attract a 

 crowd" seems to require reading: "Things that would 

 fail to attract a crowd are not policemen seven feet high " 

 — a form which most children would think unnatural. 

 Indirectly the child might learn, by this system as well as 

 by any other, that the real difficulty of avoiding logical 

 blunders lies more in translating ordinary language into 

 carefully-defined symbols, than in the operations after- 

 wards performed by merely mechanical rules. But 

 teachers who desire rather to show by diagrams the direct 

 binding force of deductive reasoning would do well to 

 select for illustration those propositions which can be 

 most simply and naturally regarded as expressing the 

 " extensive " comparison of classes. It is only fair to Mr. 

 Lewis Carroll to add that the examples he provides for 

 exercise will not perhaps do more to keep alive the notion 

 that logic is trivial than many of those that are given in 

 perfectly sober text-books. As things are, the junior 

 student seems, not unnaturally, to believe that the safest 

 plan of answering logical conundrums is to find out the 

 most ingenious and roundabout way of avoiding the 

 answer that would be dictated by common-sense. It is 

 worth considering whether the correction of this tendency 

 is not a more pressing need in the teaching of elementary 

 logic than even the best new variations on the old sur- 

 prise of finding that absurdity in matter is no bar to 

 legitimacy in form. Alfred Sidgwick. 



OLTR BOOK SHELF. 



Nitrate of Soda : its Importance and Use as a Manure. 

 A Prize Essay. By A. Stutzer, Ph.D., re-written and 

 edited by P, Wagner, Ph.D. (London : Whittaker and 

 Co., 1887.) 



In the spring of 1885 a committee of South American 

 nitrate of soda manufacturers offered a prize for the best 

 popular essay on the above subject. The judges were 

 Profs. Grandeau (France), Adolf Mayer (Holland), Peter- 

 mann (Belgium), Thoms (Russia), P. Wagner (Germany), 

 and Mr. Warington (England). The prize was divided 

 between two of the competitors, Dr. A. Stutzer, President 

 of the Bonn Agricultural Experiment Station, and Prof. 

 Adolphe Damseaux, of Gembloux. 



The book now presented embodies the main points of 

 Dr. Stutzer's essay, combined with the views expressed by 

 the committee of judges, and important matter contained 

 in the second prize essay. The subject is divided into 

 two parts, in the first of which theoretical questions as to 

 the advantages to be derived from the use of nitrate of 

 soda are ably and thoroughly sifted, and the error of many 

 popular prejudices is exposed. The important question 

 of the impoverishment of the soil is carefully discussed, 

 and the conclusion arrived at that it causes an increased 

 consumption of nutrient substances only in proportion to 

 the increase of crop, and does not increase the percentage 

 of potash and phosphoric acid in the crop, and even that 

 a larger crop is produced with proportionally smaller use 

 of the two latter materials. It is also shown that, although 

 nitrate of soda does cause a large increase of straw, yet 

 it quite as certainly causes an increase in the quantity of 

 grain. 



The second portion of the book contains very clear 

 instructions for the use of nitrate of soda with various 

 crops, and will prove a capital practical guide for farmers. 



A. E. T. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he under- 

 take to return, or to correspond with the writers of, 

 rejected manuscripts. Mo notice is taken of anonymous 

 C0171 niunications. 



\_The Editor urgently requests correspondents to keep their 

 letters as short as possible. The pressure on his space 

 is so great that it is impossible otherwise to insure the 

 appearance even of communications containing interesting 

 and novel facts.'] 



Units of Weight, Mass, and Force. 



In a letter to Nature, dated March 29, 1 stated that we have 

 "no names for units of velocity, acceleration, impulse, momentum, 

 &c." This cannot be said now. Through the kindness of Messrs. 

 Macmillan and Co., I have, this morning, received a copy of 

 "Dynamics for Beginners," by the Rev. J. B. Lock, M.A. In 

 this book the units of velocity and of acceleration are named 

 a velo, and a celo, respectively. Other units also have received 

 names, " the use of which " (as the author justly observes) " will 

 be found to simplify considerably the language of the subject." 

 The preface to this book is dated April 1887. 



Bardsea, April 23. Edward Geoghegan. 



Earthquake in the Western Riviera. 



An interesting fact in connexion with the late disastrous 

 earthquake which did such damage along the Western Riviera 

 of Liguria on the morning of February 23 last, and with which I 

 only lately became acquainted through my friend Dr. Bellotti, of 

 Milan, who was at Nice at the time, is that during the days im- 

 mediately following the catastrophe quite a large number of 

 deep-sea fish were taken dead or half dead in shallow water or 

 found stranded on the beach. This happened more especially in 

 the immediate neighbourhood of Nice, whose sea, as that of 

 Messina, has long been well-known for its richness in deep-sea 

 fish. 



I have since taken the pains to inquire more fully into the sub- 

 ject, which has a very special interest for me, and through Gal freres 

 I have learnt that the following species were taken : Alepo- 

 cephalus rostratus (mostly dead and floating), numerous ; Poma- 

 tomus telescopium, several; ■ Tetragonurus cuvieri, one speci- 

 men ; Dentex macrophthalmus, many ; Scopelus elongatus, 

 several ; Scopelus humboldti, several ; Spinax niger, abundant. 



Alepocephalus rostratus is a typical deep-sea form, only found 

 as yet, and rarely, during the summer along the Western 

 Riviera by deep-sea liners. 



Several of the fish above mentioned are in my possession. 



Firenze, April 20. ; Henry H. Giglioli. 



f The Boiling-Point and Pressure. 



A very convenient lecture experiment to show that the boil- 

 ing-point of liquids is lowered by diminishing the pressure of the 

 surrounding medium, may be made with one of Ducretet's carbon- 

 dioxide tubes. The lower part of the tube contains the COg in 

 the liquid condition, while the upper part is, of course, filled 

 with the same body in the gaseous state. By subjecting this 

 upper half of the tube to a jet of ether spray, the pressure of the 

 inclosed gas will gradually diminish, and after a few seconds the 

 liquid below will enter into brisk ebullition. 



The experiment is readily adaptable for projection on a 

 screen. M. F. O'Reilly. 



St. Joseph's College, Clapham. 



A Sparrow chasing Pigeons. 1 



Mr. J. JENNER Weir (Nature, vol. xxxv. p. 584) says that " 

 he has never observed a sparrow to chase a pigeon except when 

 on the wing. 1 wish to say that I have frequently witnessed the , 

 occurrence, having kept pigeons for a number of years. I havei 



