Re/lection and Refraction of Light. 204 



the earth, be so exhausted by expansion, that we might consider their 

 action even on the delicate organ of the eye, as perfectly insensible ; at 

 any rate, it does not seem probable that the immensely distant fixed stars 

 could exhibit their brilliancy : but the elasticity, according to the theory, 

 must be imperfect} how then can we look for effects so great, from a cause 

 comparatively so minute ? It is not without good reason that Sir J. 

 Herschel observes : " Certain admissions must be made at every step, as 

 to the modes of mechanical action, where we are in total ignorance of the 

 acting forces ; and we are called on when reasoning fails us, occasionally 

 for an exercise of faith." Treatise on Light, art. 565. He adds, "The 

 undulatory system especially is necessarily liable to considerable obscuri- 

 ties ; as the doctrine of the propagation of motion through elastic media is 

 one of the most abstruse and diflScult branches of mathematical enquiry, 

 and we are therefore perpetually driven to indirect and analogical reason- 

 ing, from the utter hopelessness of overcoming the mere mathematical 

 difficulties inherent in the subject, when attacked directly." 



If G DB, fig. 2, be considered as a wave propagated from S ', then each 

 point of it will propagate waves in all directions j but Sir J. Herschel has 

 shewn, Treatise on Light, art. 628, 629, that, the direct rays only are 

 eflScientto illuminate any point, at 5,- because the secondary waves excited 

 at a moderate distance from D nullify each other's effects by interference. 

 Now the same arguments will shew that any small object illuminated by 

 the whole of the sun's disk would be equally illuminated by a small portion 

 of it, as suppose the ten thousandth part, because the waves propa- 

 gated from the exterior regions, being in every imaginable phase, will 

 counteract each other's effects, leaving only the direct light sensible. Similar 

 observations might be made respecting waves of light thrown by refraction 

 to a focus. These observations are by no means intended to oppose the 

 principle of interference of light, that principle is founded in nature and 

 fact, and is of extensive application ; yet it is not that every thing, which 

 it is made in support of the undulatory theory. 



19. We proceed to explain the same fundamental facts on the simple 

 principles of the new theory, as stated in the 7th and 8th articles above. 



Referring to art. 9, 1 0, and 1 1, it will be manifest that an immense number 

 of etliereal atoms attach themselves to the surfaces of the sphere of re- 

 pulsion of each tenacious atom, forming on it an atmospherule, in which 

 the centres of the ethereal atoms are retained within the sphere of each 

 other's repulsion, in consequence of the superior force by which they are 

 attached : now it is very manifest, that if the central atom were at once 

 aiiiiihiiated, these ethereal atoms, being freed from the retaining force, 

 would be projected in all directions by their mutual repulsions ; and, be- 

 cause of their very small masses, they would separate with very great 

 velocities. The same thing will occur in every case of energetic chemical 

 combination : for, in this case, two or more central tenacious atoms, 



