538 



SCIENCE. 



[Vol. IX., No. 226 



monument, during thunder-storms. The apparatus 

 used consists of a large insulated collector, a modi- 

 fied Mascart electrometer, and Mascart insulators 

 and the necessary adjuncts. As the thunder-clouds 

 approach, the electrometer-needle becomes very ac- 

 tive, and, after considerable oscillation, begins to 

 move steadily in one direction (generally negative), 

 until a deflection indicating, for example, a potential 

 of three thousand volts, is reached, when, simultane- 

 ous with a flash of lightning, occurs a quick drop to 

 zero, to begin again slowly to increase, and then 

 more rapidly, until the next flash of lightning. So 

 perfect is this correspondence, that the lightning can 

 be timed as accurately from the indications of the 

 electrometer as by direct vision. If at this time a 

 finger be held out towards the collector, sparks are 

 given, with the accompanying crackling and hissing, 

 and the tingling sensation in the finger. In such a 

 case, the observer is simply grounding the insulated 

 charged collector. The greatest sparking distance, 

 in our experience thus far, as determined by direct 

 measurement, was a little under four millimetres. 

 I have never found any difference (as one of your 

 correspondents intimates) in the sparking distance, 

 depending on the finger. The potential of the air, 

 however, as shown by the electrometer readings, is 

 constantly fluctuating, often very rapidly, and at 

 certain times the potential of the air is zero. Of 

 course, a finger presented at such a time, fails to 

 draw a spark. 



To imitate more closely the conditions of the 

 mountain-side, the previous arrangement was re- 

 versed, and the observer insulated by standing on a 

 Navajo blanket folded several times. This is but 

 poor insulation, though it answered the purpose. 

 Standing close to the open window of the monument, 

 the results were as anticipated. My hair stood on 

 end, and, on presenting a knuckle to the iron frame- 

 work, a spark passed. I should remark that these 

 effects were only experienced during a thunder- 

 storm. I tried the experiment at other times, with- 

 out success. 



There are two further points of interest to which 

 attention is called. Professor LeConte has instanced 

 {Science, ix. No. 205) the case of the survey party on 

 one of the San Juan mountains, where " a sudden ces- 

 sation of the distressing electrical effects was experi- 

 enced whenever there occurred a flash of lightning." 

 This is confirmed by what precedes ; and our elec- 

 trometer readings make it certain that every light- 

 ning-flash relieves the electrical tension, and gives us 

 also the means of estimating the electromotive force 

 producing the disruptive discharge, and the electric 

 strength of the air, under natural conditions. The 

 second point of interest is the effect of electrifica- 

 tion upon the water-particles present. Lord Kayleigh 

 has shown how the character and direction of a fine 

 stream of water may be altered by electrical in- 

 fluences ; for example, a stick of sealing-wax, when 

 rubbed, distorting a fine jet of water. Effects of the 

 same character I noticed in the jet of water issuing 

 from the nozzle of the collector. When the collector 

 was ' grounded,' the stream would preserve a certain 

 even, rounded character, breaking into drops some 

 four inches away from the jjlace of issue. Remov- 

 ing the ground connection, the stream would twist 

 and split into sprays with the increasing electrifica- 

 tion. Simiiltaneous with a flash of lightning, this 

 distortion ceased, and for the moment the stream 

 resumed its first character, only to be again distorted. 



and repeat the same operation with the next light- 

 ning-flash. Alexandee McAdie. 

 Cambridge, May 25. 



Railway jubilee, Paris, 1887. 



I am requested by the executive committee in 

 Paris to ask the favor of appealing through your 

 columns for the loan of any objects, books, medals, 

 drawings, etc., relating to the history of railways, 

 and means of transportation generally, both ancient 

 and modern, in this country. 



I am directed, also, to say that all expenses of 

 forwarding and returning the same to the lenders, 

 packing and unjpacking, will be defrayed by the ex- 

 ecutive, that each object will be insured for the 

 value the lender may put upon it, and that special 

 attendants will be told off for their safe custody. 



All communications on the subject may be ad- 

 dressed to M. G. Senechal, 8 Faubourg Montmartre, 

 Paris, or to Mr. George L. Fowler, M.E. (of New 

 York City), commissioner in charge for the United 

 States, Palais de I'Exposition, Bois de Vincennes, 

 Paris, France. By addressing communications 

 direct to Paris, much valuable time will be saved. 



John W. Weston. 

 Chicago, 111., May 23. 



The maxillo-palatines of Tachycineta. 



With respect to what your correspondent says in 

 regard to a drawing of mine, I can only say that the 

 skull of T. thalassina from which it Avas made is a 

 perfect one, and my copy correct in all particulars. 

 This is more than I can say for the reproduction of 

 it {Science, No. 223, flg. 1) ; but however this may 

 be, it at least affords me now the opportunity to 

 yield gracefully to my critic, for I am free to confess 

 that the maxillo-palatines of that skull are ' im- 

 perfect ' and ' broken off ' — on paper — by Mr. F. 

 A. Lucas ; as any one may see who cares to compare 

 my drawing in the Proceedings of the Zoological 

 society of London (Dec. 1, 1885, p. 899, fig. F) with 

 his copy of it in Science, to which I refer above. 



E. W. Shufeldt. 

 Fort Wingate, N.Mex., May 20- 



No parietal foramen in Tritylodon. 



Dr. George Baur of the Peabody museum. New 

 Ha-ven, has been recently studying the fossil verte- 

 brates in the British museum of natural history. At 

 my request he has kindly made a careful study of 

 the skull of Tritylodon, and finds that Professor 

 Owen's observation of a foramen between the parie- 

 tal bones is incorrect. He writes (London, May 8), 

 "Ich habe Tritylodon hier genau untersucht, ein 

 Parietal-Foramen existirt nicht ; es ist wenigstens 

 keine Spur desselben nachweisbar." This contra- 

 dicts, without question, the suggestion I made in a 

 recent number of Science, upon the strength of Pro- 

 fessor Owen's observation, that there was probably a 

 pineal eye of considerable size in Tritylodon. I 

 hasten to make the correction, before the suggestion 

 goes any further. Although it has proved incorrect, 

 I think any one who will examine Professor Owen's 

 figure and description of the Tritylodon skull {Quart, 

 journ. geol. soc, 1884) will admit that there was suf- 

 ficient ground for this conjecture. 



Henby F. Osboen. 

 Princeton, N. J., May 26. 



