402 Memoranda respecting Experiments io ascertain 



ference existed between the time of the sun's appearing to rise 

 to a spectator situated in any given place, and to another «tand^ 

 ing two miles fnrther off to the westward. Our present ac- 

 quaintance with the astonishing rate at which, it moves makes 

 us almost smile at the attempt to discover it bv such inefficient 

 means ; but without experiments, nothing can be known with 

 certainty. 



We are indebted for our knowledge of this important fact to 

 the invention of telescopes. Mr. Olaus R5mer foimd it from ob- 

 servations of the eclipses of Jupiter's satellites made at diiTcrent 

 distances of that planet from the earth ; and we are now informed 

 that light travels from the sun to us, a distance of 95 millions of 

 miles, in about S' 13" of time. 



Mr. Boyle, who was indefatigable in his attention to every sub- 

 ject of importance connected with chemistry and natural philo- 

 sophy, has informed us of a great number of curious experiments 

 which he made on light and colours ; and even at present, al- 

 though our acquaintance with the su'oject has proceeded so 

 much further, his work is extremely interesting. 



It is, however, to the -great Sir Isaac Newton that we are in- 

 debted for the most valuable knowledge which we possess of 

 the different proj^erties of light and colours. By making a pencil 

 of rays pass near the edge of any sharp body, as that of a knife 

 or broken glass, he proved that they were bent or inflected ; and 

 by making the rays pass through glass ))risms, and receiving the 

 .spectrum at a distance, he found light to be a heterogeneous 

 mixture of differently refrangible ravs ; and that there are as 

 many simple or homogeneal colours, as there are degrees of re- 

 frangibility ; for to every different degree of rcfrangibility belongs 

 a different degree of "colour. 



The ideas of philosophers respecting the nature of colours be- 

 fore the time of Newton are extremely hypothetical, and unsup- 

 ported by the least attempt at experimental proof. It may 

 therefore easily be conceived what pleasure was gi\en to the 

 lovers of truth, by so extensive a pursuit of the subject as was 

 published in his treatise of Optics. After he had thus developed 

 the true theory of light and colours, he then proceeded to ex- 

 plain all their properties and phenomena, in so satisfactory a 

 manner that his investigation has justly been considered as the 

 best model for guiding al! future inquiries into the laws ofNature, 

 With regard to tiie absorption of warmth from coloured rays, — 

 the object of our present consideration, — Mr. Boyle caused a large 

 block of black marble to be ground into the form of a spherical 

 concave speculum ; and found that the sun's rays reflected from 

 it were far from being too powerful for his eyes, as would have 

 been the "case had it been of any other colour; and although 



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