David Forbes — Mepli/ to Dr. T, Sterry Hunt. 109 



All the other points have been noticed in my recent communication 

 to the Chemical News, and I would merely state here that as regards 

 Dr. Hunt's criticisms upon my views it is probable that many of 

 them would not even have been advanced by Dr. Hunt had he 

 waited until the outline of my views on Chemical Geology,, now in 

 the press, had appeared, instead of selecting scattered and disjointed 

 sentences for attack, without giving the context. Thus, for example, 

 when he accuses me of being ignorant of the laws of diffusion, he 

 would have found my opinions expressed as follows : — 



" Whilst, on the one hand, the zones formed in the earth are con- 

 sidered to have possessed a somewhat stable or permanent character, 

 those formed in the atmosphere would, on the contrary, be the reverse, 

 for no sooner had the gasiform products forming them, by in the first 

 instance obeying the impulse of gravity so overcome the counter- 

 acting tendency of the laws of diffusion of gases, than these latter 

 would assert themselves, and, in process of time, entirely obliterate 

 this arrangement." 



And again, " as before stated, this arrangement would be gradually 

 obliterated by diffusion, but, as the element of time is of vital im- 

 portance in considering the effects of diffusion, it is imagined that, 

 before being obliterated, this arrangement may have had considerable 

 influence in modifying the chemical re -actions which took place at 

 this period in the earth's history." 



Dr. Hunt, whose knowledge of the laws of diffusion does not seem 

 to include any appreciation of the importance of the element of time 

 in their consideration, might just as well tell us that a lump of sugar 

 could not reach the bottom of a tumbler of water because sugar 

 will dissolve in water. As Dr. Hunt seems to have such respect 

 for authorities on the subject, I will, with the greatest pleasure, 

 submit the question, whether the above proposition is invalidated by 

 the action of the laws of diffusion, to the decision of Mr. Graham, 

 the great expounder of these laws, and abide by his verdict.' 



In the discussion of new views, more is required than mere quota- 

 tions from old authorities. What is specially wanted are facts and 

 experimental evidence. It must also be remembered that much de- 

 pends upon the mode in which authorities are made use of in such 

 discussions, since it is often an easy matter to select passages, or 

 disjointed fragments, from the published works of authorities, which 

 may appear to support almost any view which may be taken of a 

 subject under consideration. 



Dr. Hunt, whose paper consists, in greater part, of references to 

 numerous authorities, from the time of Thomas a Kempis down to 

 that of Sterry Hunt, seems to be quite aware of this fact, as an in- 

 stance or two will testify. 



Thus, when Dr. Hunt quotes Hopkins in support of his views as 

 to the consolidation of the molten sphere, he takes care not to inform 

 his readers that Hopkins distinctly declares his opinion that the ex- 

 terior was not the last to solidify, but would have consolidated be- 



^ It must be remembered that these gases are supposed to be formed at an instant 

 of general combination in situ, and not gradually gathered from the realms of space. 



