Astronomical and Nautical Collections* 141 



ened by a single mirror ; for it will be much more visible in 

 this latter situation than in the former, especially if the 

 room is well darkened, and if all proper precautions have 

 been taken to exclude all the light but that which is the sub- 

 ject of the experiment. 



It is then completely demonstrated, that, in certain cases, 

 light added to light produces darkness. This capital fact, which 

 did not escape Grimaldi, although Newton seems to have 

 been ignorant of it, had been sufficiently proved in our own 

 times by the experiments of Dr. Young ; but the phenomena 

 which I have related afford perhaps clearer evidence of its 

 truth, because the dark stripes that it exhibits are, in gene- 

 ral, blacker than those which are produced by diffraction, 

 properly so called, and because it supersedes every idea of 

 the operation of a diffractive force, which might be supposed 

 capable of expanding the beams of light in some places, 

 and condensing them upon others, since the effect is here 

 exhibited by rays which have been regularly reflected. 



[To be continued,] 



The Life of Edward Je7iner, M.D., LL.D., F.R.S., Phy- 

 sician Extraordinary to the King, Sfc. 8fc. ; with lllus^ 

 trations of his Doctrines, and Selections from his Corre^ 

 ^/;o?2<i^?2C6'. j5y John Baron, M.D., F.R.S. London, 1827. 



The close of the eighteenth century was rendered memorable 

 by the promulgation of a fact in the natural history of man, 

 the consequences of which have been, and continue to be, of 

 a magnitude quite incalculable. In every habitable part of 

 the earth its effects have been felt, and are still to be wit- 

 nessed. To the physiologist, studious of the analogies that 

 subsist among the different classes of animals, it opened a 

 wide field of interesting research. The physician viewed it, 

 as giving him a power over disease greater than any which 

 medical skill had brought to light during a period of two 

 thousand years. To the cyQ of the political economist, it 

 offered the prospect of a rapid and momentous increase in 

 the population of the country. The philanthropist hailed 

 it as affording tlie certain prospect of diminisliing the sum of 

 human misery ; and to those who were content to lopk on it 

 with other eyes than those of science, a spectacle was pre^ 



