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ADDRESS OF PROFESSOR LOVERING. 623 
materials, and extracted from them two new and independent 
values for the sun’s parallax. The reconciliation which he has 
suddenly brought about between the experiments of Cornu and 
Foucault, the motions of the moon, and the transits of Venus, 
is as perfect as it is surprising. Nevertheless, the approaching 
transits of Venus, the earliest of which is close upon us, will be 
welcomed, if not as the only possible way of solving a hard 
problem, at least for the confirmation which is demanded by a 
solution already reached: for able astronomers have dissented 
ftom the interpretation put upon the records by Stone. The minds 
of observers have been prepared for what their eyes are to see, in 
December, 1874, by the experimental rehearsal of the black drop, 
and the photographer’s box will arrest the planet in the very act. 
The consequences of Foucault’s experiment, substantiated as it 
may be by the best astronomical evidence, are as far reaching as 
the remotest stars and nebulæ. The sun’s distance is the astron- 
omer’s metre, through which masses, diameters, and distances are 
Proportioned out to planets, comets, and stars. If the sun’s dis- 
tance is cut down by three per cent., there must be a general con- 
traction in all the physical constants of the universe. The earth 
only is immediately exempt from this liability. But if, as modern 
“lence teaches, the earth lives only by the triple radiation from 
the sun, then an earlier doom has been written for the earth also. 
: logy is no longer allowed to cut its garment from a past dura- 
ton of unlimited extent. The numerical estimates of physical 
_ “lence, with a large margin of uncertainty, assign limits between 
“hich alone geology has free play. Whatever tends to reduce or 
those limits must be of interest to the geologist as well as 
to the astronomer, 
This is the brilliant career, in electricity, optics, astronomy, and 
geology, of the little mirror, cradled in the laboratory of Poggen- 
dorf, ana which has not yet seen its fiftieth birthday. 
Making this exhibit of the instrumental appliances of modern 
. sics, I will simply name the polariscope, the stereoscope, and 
“ instruments in photography, and hurry on to the spectroscope. 
“© steps by which the spectroscope has attained its preeminent 
; E among the instruments of the physicist and the astronomer 
ere taken at long intervals. A whole century intervened between 
*wton’s experiments with the prism and Wollaston’s improve- 
Ment. The substitution of a long and narrow slit for the round 
