‘ 
a 
: 
d 
Chemistry and Physics. 397 
3. Efficiency of Spectroscopes.—F. Lippicn discusses the point 
whether it is more advantageous to increase the dispersion or to 
increase the magnifying power of the telescopes of a spectroscope. 
mathematical discussion of the subject is given and the follow- 
eached i i it i 
times. Seven lines are 
tween the D lines.— Centrail-Zeit. f. Opt. u. Mech., 49 and 61, 1881. 
Ee 
4. Niagara Falls as a source of Energy.—Sir Wu. Tuomson 
thus sums up, in his British Association Address, the conclusions 
he has reached in regard to the utilization of the energy of 
Niagara Falls. 
“1. Apply dynamos driven by Niagara to produce a difference 
of potential of 80,000 volts between a good earth connection and 
the near end of a solid copper wire of half an inch (1°27 centime- 
ters) diameter, and 300 statute miles (483 kilometers) length. 
“2. Let resistance by driven dynamos doing work, or by elec- 
tric light, or, as I can now say, by a Faure battery taking in a 
charge, be applied to keep the remote end at a potential differing 
by 64,000 volts from a good earth plate there. 
“3. The result will be a current of 240 webers through the 
wire taking energy from the Niagara end at the rate of 26,250 
horse power, losing 5,250 (or 20 per cent) of this by the generation 
and dissipation of heat through the conductor and 21,000 
power (or 80 per cent of the whole) on the recipients at the far end. 
“4. The elevation of temperature above the surrounding atmos- 
wire supported on posts. : : 
“5. The striking distance between flat metallic surfaces with 
difference of potentials of 80,000 volts (or 5,000 Danuiells’) is only 
eighteen millimeters, and therefore there is no difficulty about the 
Insulation. : 
“6. The cost of the copper wire, reckoned at 8d. per pound, is 
37,0002, the interest on which at five per cent is 1900/, a year. 
If 5,250 horse power at the Niagara end costs more than 19004. a 
year, it would be better economy to put more copper into the 
Conductor; if less, less.” —Nature, Sept. 8, 1881, p. 435. J.T. 
5. Change of plane of polarization of Heat rays by Electro- 
magnetism.—LEo GRUNMACH reviews the work of previous expert- 
menters and arrives at the following conclusions: 
