January 22, 1892.] 



SCIENCE. 



53 



advocates of the concussion theory welcome any discoveries that 

 can add to our knowledge of the reasons why battles cause rain, 

 and thus suggest methods for producing it which may be an im- 

 provement on these suggested by the battles and their sequences. 

 In this category appears to be the discovery of Mr. Aitken referred 

 to, but it furnishes nothing conclusive on the subject, and, in my 

 opinion, an experiment on the line marked out by Professor Blake 

 would prove a failure. If some of us go to one extreme in relying 

 too much on concussion as the means by which the process of nature 

 that leads to rain can be set in motion, so does Professor Blake go 

 to the other extreme in holding that it is smoke or dust particles 

 alone that can artificially effect that result. We know, as a mat- 

 ter of fact, that simply throwing smoke into the air does not pro- 

 duce rain. There are scores of cities in our land whose chimneys 

 are doing this every day, and yet they do not produce rain. And 

 it cannot be said that the smoke they send up is not of the right 

 kind. It contains a great deal of sulphur and of carbon, and 

 these, according to Prosessor Blake, are among the substances 

 which form dust particles, around which molecules of aqueous 

 vapor most readily collect. 



In the light of Mr. Aitken 's discovery, however, I am willing to 

 admit the possibility that smoke may not be without its effect in 

 producing the rain that foUou's battles — an idea, I may add, 

 which, though not original with me, I placed on record over 

 tvrenty years ago, as may be seen by reference to the letter of 

 Gen. Robert A. McCoy, in the appendix to "War and the 

 Weather." In any future experiments in the field the application 

 of the principle discovered by Mr. Aitken ought to be duly tested. 

 But I see no reason as yet for doubting that force, exerted by 

 means of explosions and expended on the earth and air, is a nec- 

 essary factor in ai'tificial rain production. 



Edward Powers. 



El Paso, Tes., Jan. 15. 



since by a lady nearly eighty years old. She had recently had 

 one eye treated for cataract, and was told to test the perceptive 

 power of it. In order that there might be no interference by the 

 other eye, this was covered by the hand. 



This habit of peeping, or looking with one eye open and the 

 other closed, is plainly an acquired one, becoming easy by prac- 

 tice, as is seen by comparing children with adults, and men and 

 women with each other. Tlie difference in the latter is mostly due 

 to the lack of use. Boys early become accustomed to " sighting " in 

 various ways in their play, as in the use of the cross-bow or bow 

 and arrow, toy gun or real gun, or they may wish to line some- 

 thing. They also work more with tools, and, like a carpenter, 

 must see it they are making a straight edge, and thus acquire this 

 ability. There being less occasion for it on the part of girls and 

 women, they may fail to gain it at all. This is not from inherent 

 inability any more than in the case of men, \m.less heredity be- 

 comes a factor working through sex, and facilitating the process. 



E. J. Hill. 



Englewood, Chicago, Jan. 14. 



Eye-Habits. 



Ik Science of Dec. 18, 1891, p. 339, is a note taken from Nature, 

 and referring to some experiments of Mr. James Shaw to test the 

 ability of school children to keep one eye open and the other shut 

 at the same time. Having been associated with school children 

 for many years where the microscope was frequenlly used in the 

 class-room for demonstration, my attention has often been called 

 to their proceedings in this respect, and the impressions may be 

 worth recording, though they are, no doubt, essentially like those 

 of many other teachers in analogous positions As the use of the 

 microscope was only for a short time to each individual in a par- 

 ticular exercise, it was necessary that an observer looking into the 

 tube of a monocular should by some means close one eye in order 

 that other objects might not be in the field of view of the unoccu- 

 pied eye and confuse the image. For it requires long practice on 

 the part of one using a monocular stand to examine an object 

 while keeping both eyes open and not be inconvenienced, a train- 

 ing out of question with school children where the time was lim- 

 ited. In the case of such the eye was closed either with or with- 

 out the use of the hand. Being pupils in a high school their ages 

 ranged from fourteen to twenty or more, the majority from fif- 

 teen to eighteen. Statistics were not kept, but I do not recall an 

 instance where a boy could not close one eye without the aid of 

 the hand. If it occurred, it was very rare. But it was quite 

 common for girls to make use of the hand for this purpose, a 

 fourth or more, as mentioned by Mr. Shaw for school children. 



Sometimes, by request of teachers in primary grades, I have 

 taken a microscope to their rooms, in which the lowest classes 

 were taught, their ages being from six to eight or nine. It was 

 for the purpose of showing something which the teachers desired 

 to use as an object-lesson, like the eye or foot of a fly, or the scales 

 from the w ing of a butterfly, things whose forms they readily 

 comprehended, as was shown by their description of them. With 

 them the unaided closing of one eye was exceptional, some of the 

 older boys, perhaps, being able to do so. I have noticed the same 

 difficulty with older people who occasionally look through a mi- 

 croscope; the inability to shut one eye and leave the other open 

 being among the women. This was illustrated but a short time 



BOOK-REVIEWS. 



Chambers's Encyclopcedia. New edition. Vol. VIII. Peasant 

 to Roumelia Philadelphia, Lippincott. Royal 8°. $4. 



Comment on this encyclopsedia may seem almost superfluous, 

 not only because the work is well known, but also because of the 

 uniform excellence of its several volumes; yet one does not like 

 to pass it by without remark. The present volume is noteworthy 

 for the number of its articles on philosophical and religious topics ; 

 Professor Andrew Seth writing on Philosophy, Professor D. G. 

 Ritchie on Plato, Professor Sorley on Psychology, Mr. James 

 Oliphant on Positivism, Professor Fliut on Religion, Rev. W. L. 

 Gildea on Roman Catholicism, Professor Cheyne on the Book of 

 Psalms, etc. In the very different department of the industrial 

 arts we find articles on Photography, by T. C. Hepworth and W. 

 T. Bashford ; on the Plough and the Potato, by James MacDonabl ; 

 on Pottery, by James Paton; on Printing, by John Southward; 

 and a long one on Railways, by E. M'Dermott. In science strictly 

 so called. Professor Peile treats of Philology, Mr. Norman Wyld 

 of Plants and of Physiology, Professor Knott of Quaternions, Dr. 

 Alfred Daniell of Reflection and Refraction Mr. J. A. Thomson 

 of Protoplasm and of Reproduction; while the minor articles ai-e 

 too numerous to mention. In history and geography the most 

 important papers are perhaps those on Phoenicia, by Canon Raw- 

 linson; on Rome, by Canon Taylor and Dr. Steele; and on Persia 

 and Persepolis, by Gen. R. Slurdoch Smith. In this department 

 it seems to us that there is a deficiency of maps. Political and 

 social themes receive their share of attention, Mr. T. Kirkup treat- 

 ing of Political Economy, Mi-. Jesse CoUings of Peasant Proprietors, 

 Mr. W. C. Smith of the Poor Laws, Sir E. F. Du Cane of Prisons, 

 and Mr. W. Draper Lewis of Protection. Literature and the ideal 

 arts are less conspicuous in this volume than in some of the pre- 

 vious ones; but Mr. Edmund Gosse writes of Poetry, Mr. Stead of 

 Periodicals, Sir Joseph Crowe of Raphael, Mr. P. G. Hamerton 

 of Rembrandt, and Mr. W. Holman Hunt of Pre-Raphaelitism. 

 The number of minor articles on all subjects is so great as to pre- 

 clude all mention of them individually; yet it not unfrequently 

 happens that these are the most useful of all to the reader It is 

 expected that the two remaining volumes of the Encyclopsedia 

 will appear during the present year. 



AMONG THE PUBLISHERS. 



The new volume of the Badminton Library, announced by 

 Little, Brown, & Co. for immediate publication, will treat of 

 skating, curling, tobogganing, and other out-door sports. It is 

 written by J. M. Heathcote, C. G. Tebbutt, T. Maxwell Witham, 

 and the Rev. John Kerr, Ormond Hake and Henry A. Buck, and 

 contains several plates and numerous illustrations in the text, by 

 C. Whymper and Captain Alexander. 



— John Wiley & Sons announce as in preparation " Elementary- 

 Lessons in Heat," by Professor S. E Tillman, United States Mili- 



