^ 



396 Intelligence and Miscellaneous Articles. 



platinum disks, at a distance of 40 centims., is sufficient for demon- 

 strating the passage of the electricity. The mean temperature of 

 the gas is in this case so little elevated that a person can hold his 

 hand in it ; a thermometer placed there shows a mean final tempe- 

 rature of from 60° to 70°. The interposition of a screen or the 

 agitation of the air hinders the phenomenon. The lamp can be 

 replaced by an incandescent body, such as a stout glass rod made 

 red-hot ; consequently atmospheric air itself is susceptible of 

 becoming a conductor. 1 have observed that if the two platinum 

 disks are heated unequally, considerable electromotive forces are 

 produced : the hotter disk constitutes a negative pole with respect 

 to the other. The direction of this phenomenon is the same as that 

 observed by M. Becquerel in the flame itself. — Comptes Rendus de 

 VAcademie des Sciences, April 4, 1881, t. xcii. pp. 870-872. 



ON AN ACOUSTIC PHENOMENON NOTICED IN A CROOKES TUBE. 

 BY CHARLES R. CROSS*. 



A short time since, while experimenting with a Crookes tube, I 

 noticed a phenomenon which was quite striking, and so evident 

 that it hardly seems possible that it has not frequently been observed 

 before ; but as no allusion to the effect in question has come to my 

 notice, I venture to call attention to it. 



Tn working with the tube, in which a piece of sheet platinum is 

 rendered incandescent by the concentration upon it of electrified 

 particles repelled from a concave mirror, I noticed that when the 

 mirror was made the negative electrode, so that this concentration 

 took place, a clear and quite musical note issued from the tube. I 

 thought at first that the pitch of the note would coincide with that 

 produced by the circuit-breaker used with the coil (which made 

 about 100 breaks per second) ; but this did not prove to be the case. 

 In fact, very great changes in the rate of the circuit-breaker did 

 not affect the note given by the tube. The effect seemed to be pro- 

 duced by the vibration of the sheet platinum in its own period, 

 under the influence of the molecular impact, which vibration was 

 communicated to the glass walls of the tube by the enamel rod to 

 which the platinum was attached, giving rise to a sound somewhat 

 resembling the pattering of rain against a window-pane, but higher 

 in pitch and more musical. This sound changed its character very 

 greatly when the direction of the current was reversed, a feeble 

 murmur only being heard. I obtained a similar musical note, 

 though far less loud, with the " mean free-path tube," best when 

 the middle plate was positive. With a tube containing phospho- 

 rescent sulphide of calcium, the note was very dull in its quality 

 and low in pitch, but still quite perceptible. "With this tube a 

 change in the direction of the current, as might be expected, did not 

 affect the sound produced. I did not obtain this musical note from 

 any tube that I have in which the current enters and leaves by a 

 straight wire, except in the case of a single G-eissler's tube exhausted 

 so as to give stratifications, in which it was very feebly heard. — 

 — American Journal of Otology, January 1881. 



* Read at a Meeting of the American Academy of Arts'anc 

 November 10, 1880. 



