462 



SCIEXCE. 



[Vol. VII., No. 172 



with visual lines appropriately crossed, is discussed 

 but incorrectly explained by Sir David Brewster in 

 his book on the stereoscope, many of his experiments 

 Laving been performed more than forty years ago. 



Dr. Keller seems to be affected slightly with 

 divergent strabismus ; which, however, has not re- 

 sulted, as it so often does, in the loss of power to secure 

 binocular vision. He will find the phenomena of 

 vision by optic divergence discussed in a series of 

 articles entitled ' Notes on physiological optics,' pub- 

 lished in the American journal of science for No- 

 vember and December, 1881, March, April, May, 

 October, and November, 1882. 



W. LeConte Stevens. 



170 Joralemon Street, Brooklyn, 

 May 15. 



Diathermancy of ebonite. 



Absence from home has prevented me seeing 

 sooner Science for April 30. 



In referring to my paper read before the April 

 meeting of the National academy of sciences, you 

 state, " Prof. Alfred M. Mayer, in describing recent 

 work, stated that he had succeeded, by the use of a 

 lens of ebonite, in inflaming various substances by 

 the concentration of dark rays, for which ebonite is 

 tianslucent." The statement is not what I stated 

 before the academy. The title of my paper, as pub- 

 lished by the academy, is, " On the diathermancy of 

 ebonite and obsidian, and on the production of 

 calorescence by means of screens of ebonite and 

 obsidian." 



The focus of dark rays was obtained by ' screens ' 

 of ebonite and of obsidian placed across the cone of 

 rays reflected from a large mirror, or those refracted 

 by a lens of glass of twenty inches diameter. I have 

 obtained foci of dark rays with a combination of 

 thin lenses of ebonite, but the heat of such foci is 

 not sufficient to inflame substances. 



Alfred M. Mayer. 



Hoboken,N.J., May 13. 



Pharyngeal respiratory movements of adult 

 amphibia under water. 



The letter of Profs. S. H. and S. P. Gage, in your 

 issue of April 30, induces me to recall and publish 

 an observation made by me in 1877. 



During a stay of some months in New York in the 

 summer of that year, I several times visited a 

 museum and aquarium, situated, if I remember 

 aright, on 6th Avenue. I saw there a very fine 

 specimen of Cryptobranchus Alleghaniensis about 

 twenty inches long. I watched from time to time 

 for several hours, but never saw it rise to the sur- 

 face for air. As it lay at the bottom of its clear 

 glass tank, I saw very distinctly continuous rhyth- 

 mical respiratory movements. These, however, 

 were not confined to the pharyngeal region, but 

 seemed to me to extend the whole length of the body- 

 cavity. It was a kind of squirming or wriggling 

 movement running down the body. I looked care- 

 fully for currents issuing from gill slits, but could 

 see none. 



At that time I concluded that the movements 

 served the purpose of churning up the air in the 

 lungs so as to utilize as much of the oxygen as pos- 

 sible. This seemed the more necessary in amphib- 

 ians on account of the simplicity of their lung-sac. 

 I had fully intended to draw scientific attention to 



the subject, but on returning home I could not at 

 once lay my hand on a good account of the gill ap- 

 paratus of the adult Cryptobranchus, and meanwhile 

 other things engaged aud diverted my attention. 



It might be well for those who are studying this 

 subject to at least bear in mind the suggestion that 

 rhythmic movemsnts may possibly serve to utilize 

 more perfectly the oxygen contained in the lungs of 

 animals capable of remaining long under water. 

 In my boyhood I have often waited, rifle in hand, 

 three hours for an alligator to rise ; and that, too, 

 in mid-summer, when their vitality is highest. 



Joseph LeConte. 



Berkeley, Cal., May 10. 



Absorption of mercurial vapor by soils. 



In the issue of Science for April 23, it is stated 

 (p. 370) that the mercurial-vapor remedy has, in the 

 hands of myself and assistant, failed to produce its 

 promised results as a phylloxera insecticide. 



This sweeping statement is not justified by the facts 

 given by me in the issue of this journal for Dec. 4, 

 1885, and by its further elaboration as given in the 

 ' Eeport on viticultural work,' since published. It 

 has been demonstrated by our experiments that the 

 reported total failures were due to improper mate- 

 rials used in the preparation of the mercurial mix- 

 tures, whereby the formation of mercurial vapor in 

 the soil was practically prevented, and that when 

 reasonably pure mercury is employed, and proper 

 means used for its distribution in the soil, all insects 

 within the mercurialized area died in the course of 

 from thirty to forty-eight hours at the ordinary 

 temperature, and much more rapidly at a higher 

 one. It therefore appears perfectly practicable to 

 protect vines planted in uninfested ground from at- 

 tack coming from without, by surrounding the stocks 

 with a sufficiently thick (eight to ten inch) layer of 

 mercurialized soil, which, without obstructing or 

 repelling the entering insects, will insure their being 

 fatally poisoned before they can pass through it. 

 This would leave the choice between grafting on 

 resistant stocks on the one hand, and the mercurial 

 protection on the other, in the planting of new vine- 

 yards, the cost being (in California) about the same 

 in either case ; it would also serve for protection 

 against threatened invasion, in the case of vineyards 

 already planted, since, apart from the case of open 

 soil-cracks giving access to the vine-roots, the stocks 

 are the only known route by which the phylloxera 

 reaches the root. Such are the presumptions created 

 by our small-scale experiments : how far the process 

 will prove available in large-scale practice, remains 

 to be determined by experience, but there is no 

 especial reason to question its feasibility. 



As regards, however, the treatment of ground and 

 vines already infested, our experiments tend to 

 show that the diffusion of the mercurial vapor is too 

 slow, at the ordinary soil-temperatures, to promise 

 success ; especially in the case of clay soils, which 

 absorb and render inert a large amount of mercurial 

 vapor before an effective excess can be obtained. 



It has been abundantly shown that the mercurial- 

 ized soil exerts no unfavorable action upon the 

 growth of the vine ; and there is every reason to 

 expect that an application once made will remain 

 effective during the life of the vine. 



E. W. HlLGARD. 



Berkeley, Cal., April 8. 



