November 3, 1893.] 



SCIENCE. 



249 



again and with more care. Though Mr. Sumner ha» con- 

 siderable ability in certain lines yet his youth and lack of 

 special training should prevent him from criticising ideas 

 acquired by considerable study and experience. Criti- 

 cisms should be made with care. 



Albert Schneider, M. T). 



Weston, 111., Oct. 26. . 



Slate Black-Boards. 



Attention has been called to the fact that light is re- 

 flected from slate black-boards in an injurious manner. 

 One city superintendent informs the writer that he has 

 been compelled to lessen the amount of work to be copied 

 from the board. A county superintendent writes that 

 he cannot sit in a certain high school without experienc- 

 ing painful sensations, if he faces the slate boards. 



Have other teachers observed the same ? Is a slate 

 board more trying to the eyes than slated surfaces ? Is a 

 slated surface to be preferred to a true slate board ? 



Will not superintendents and teachers who care for the 

 general health of the children in their charge, and 

 especially for the eyesight of the children, communicate 

 with the subscriber in reference to this matter ? Answers 

 to the questions are earnestly solicited. Address, 



Dr. Geo. G. Gkoff, 



Lewisburgh, Pa. 



A Grooved Axe in a Strange Place. 



Some months since while making observations with Mr. 

 Haldeman O'Connor, of Harrisburg, on an island in the 

 Susquehanna, not far from the city, we came across a per- 

 pendicular exposure of a clay b'ed, from the face of which 

 several feet of earth had been removed by a recent flood. 

 Several bowlders were imbedded in its face and one of 

 them, eight feet from the top, on account of its peculiar 

 shape, attracted attention, and on removal proved to be a 

 grooved axe, well made of a heavy, close-grained sand- 

 stone, about six and a half inches long and two and a half 

 inches wide, having a good cutting edge and a perfect 

 groove — somewhat weathered but not differing in any 

 particular from the many found on the surface. The bed 

 in which the implement was found is a compact clay, the 

 lowest and the last of the terrace deposits of the valley 

 and consequently, geologically speaking, comparatively 

 recent. 



Any method, save one, to account for the presence of 

 the axe in this position, was of no avail. The clay bed 

 seemed to be unquestionably undisturbed, and no theory 

 of trap roots nor upturning of trees would explain it. 

 Did the axe find this resting place — eight feet below the 

 surface — during the deposit of the bed ? If it did its 

 maker, whoever he was, must have lived about the same 

 time, — some thousands of years ago, when the last of the 

 prehistoric floods swept down this old valley, and the 

 origin of Neolithic man, if such he was, must be placed 

 at an early date. Hakvey B. Bashohe. 



West Fairview, Pa., Oct. 1. 



mosquito, eepecially the female, in which mandibles and 

 maxillaa are said to be well developed. The first state- 

 ments are correct; but I must take issue with Dr. Packard 

 on the statement that the mandibles are well developed 

 in the mosquito, for, as a matter of fact, there is no trace 

 of these organs in that insect- All the piercing and envel- 

 oping structures are, as I have shown, homologous with 

 other mouth structures. It is further stated that the max- 

 ilke are usually much reduced, while the labium is enor- 

 mously developed and highly modified. I have, I think, 

 shown very conclusively that the enormous development 

 in the Dipterous mouth parts takes place in the maxillary 

 structures and that the labium is in most cases very much 

 reduced if not entirely wanting. The best development 

 of this latter organ is seen in the piercing flies related to 

 Tabanus, in which we are able to trace every part of the 

 normal structure of the labium of a mandibulate insect. 

 Dr. Packard's article reads as if he partially accepted and 

 partially rejected my conclusions concerning the mouth 

 structures of the Diptera, and I would be rather interested 

 to know how far he considers my conclusions in that , 

 order well founded. The reference to the mouth parts is 

 really not needed in order to support his claim, and in 

 some directions the Dipterous mouth is certainly very 

 much more highly specialized than that of the Hymenop- 

 tera. John B. Smith, 



Rutgers College, November ist. 



The Systematic Position of the Diptera. 

 In ScienceT^o. 558 for October 13, Dr. Packard has an ar- 

 ticle upon this subject, in the general conclusions of 

 which I most heartily agree. Dr. Packard has not men- 

 tioned, by any means, all of the arguments in favor of his 

 view, and some of these will be, I hope, presented by Dr. 

 Riley, who has already suggested them in lectures,, al- 

 though they are not, so far as I am aware, published. 

 There are a few points upon which Dr. Packard's pajjer 

 is not entirely clear, or where, at least, I do not seem to 

 be able to understand him entirely. He mentions, in one 

 place, as characteristic of the Diptera the "abolition of 

 mandibles (Simulium excepted). " In another place, the 

 fact that the jaws are wanting, and finally speaks of the 



BOOK-REVIEWS. 



A Guide to Stereochemistry, based on lectures delivered at 

 Cornell University, with an index to the literature. By 

 Arnold Eiloaht, Ph.D., B.Sc. New York, Alexander 

 Wilson, 26 Delancey street. 96 p. With appendix, paj)er, 

 8vo., 111. $1.00, postage free. 



The want of a suitable text-book upon this deeply in- 

 teresting new branch of chemistry, the geometrical relations 

 of atoms in sj)ace, has long been felt. The literature is 

 widely scattered and so fragmentary as to make such a 

 "Guide" as this offered by Dr. Eiloart of utmost value to 

 student and professor alike; to the latter as an aid in 

 the preparation of his lectures and to the former as a 

 digest of these lectures, with an indication of the lines 

 and means for more extended study. Unfortunately, in 

 many colleges this department of research is barely 

 touched upon, not for lack of interest, however, but be- 

 cause with the limited time commonly at the disposal of 

 the professor detailed correlation even of the work in 

 this field is an impossibility. 



While the study of structural isomerism dates from 

 1824, the actual development of stereochemistry begins 

 about 1873 — a retardation of extraordinary length, con- 

 sidering the easy step from one to the other. Isomerism 

 conceives of compounds containing the same elements in 

 the same proportions, and yet differing in proiser- 

 ties, this difference being due to a different group- 

 ing of these elements. Geometrical isomerism con- 

 ceives of compounds containing the same elements 

 in the same proj)ortions and arranged in the same groups 

 and yet differing in properties because of a different ar- 

 rangement in sjMce of the constituent groups. The sec- 

 ond conception is thus a natural outgrowth from the first. 

 Dr. Eiloart passes with a few words the accepted facts of 

 stereochemistry giving more particular attention to the 

 living issues and more daring developments. The index 

 to the literature is most carefully planned and is more 

 than a mere list of titles, insomuch as it gives by means 

 of suitable abbreviations an idea of the contents of the 

 papers referred to. An appendix with photographic 

 plates, five in number, treats of the use of "Solid Formu- 

 Ite," or models in the teaching of organic chemistry. The 

 book is copiously illustrated throughout with diagrams 

 and woodcuts. C. P, 



