254 Scientific Intelligence. 
of the plate adjacent to these will alone move the air with concordant 
impulses. now the card (or the plate) be rotated n’ times a second, 
the intensity will ae n’ periods per second ; if the amplitude of the 
original vibration of the plate be a, the amplitude corresponding to the 
rotation of the card be a’, and the pitch of the tone of the plate n, we 
have a=a’sin 2n/zt, and hence the original tone Aa sin 2n7¢ becomes 
“4 
A=a’ sin 2n'zt sin onnt=— cos 2(n — n/) mt a cos 2(n--n')xt, 
that i is two tones of pitch n—w and n-+-n' (or a aa and a higher tone) 
heard instead of the primary tone of pr ; 
Thus Stefan found that a plate giving ihe oe Jisy, which according 
to Quincke’s table (this Journal, Nov. 1866, p. 417) corresponds to 
185=—n vibrations, produces, when rahe otations per second, the tones 
F,=174°6 and g,=196, which are very nearly 1852-10. “L'Tnstitut 
gives fis,, ete., no doubt by a mistake in translating Stefan’s German 
notation. ~_T} Institut, 1866, No. 1710, p.327; Cosmos, 1866, era iv, » Pr. 
458, 4 
14. Foucault's silvered oljectives for observations of the sun. sath very 
a method for close observation of the solar disc was communi- 
ted by Foucault in September, 1866. Peorin noticed that no heat 
rays were reflected, as also the greater part of the light, 80 sO as wer permit 
only a pale bluish-violet to pass through. LeVerrier reported, October, 
1866, most favorably as to the results obtained by a 9-inch refractor 
sent cause ‘of error. “Furthermore vocal the ultra-red rays are really ab- 
sorbed ; all others are, as the prismatic spectrum show ws, vines diminished 
in intensity so as to give a steady (calme) and pure image of the sup, 
showing all detail of outline and color with excellent definition, and per 
mitting a magnifying power of 300.—Z’Jnstitut, 1866, pp. _ pes 
Cosmos, 1866, iv, 387, 430. 
15. Lead-thallium ylate has greater density and lentiagnst power than 
common lead-flint glass; 300 pure sand, 200 minium, and 3 eset 
ate of thallium (instead of the usual 100 carbonate of corde give 
glass of density 4°235, index of refraction 1-71, and only very slight y a 
lowish tint. It has been made in England —L'Institut, 1866, p. 320. 
. Expansion of water and mercury ; A. Marruressew.—The results 
of this very elaborate investigation are—the volume of water at aby 
temperature ¢° C. is V==a~—bi+ct? —dt3, the volume at 4° C. being 
the coéfficients 
for 4°<t<32 for 32<t°<100° 
rooo1s8isi28 poonens ms 
6:000000 
o-0uo00752824 00000054724 
000000007173 0000000011260 
Ro eR * 
