Mr Blackadder on Vertical and Lateral Mirage. 13 



substances with it. In Nature, we must suppose that various contaminat- 

 ing substances would in like manner occur, to diversify the phenomena; 

 and, accordingly, we do find a boundless variety, in the aspect not only of 

 sandstone, buc of almost every kind of rock; and I am by no means with- 

 out expectation, that, in the course of time, we shall be able to imitate in 

 our laboratory as many of these varieties as we choose to exhibit. 



I have long been engaged also in a series of experiments on the forma- 

 tion of Crystallites, the name by which, as I have before stated, every 

 crystallised rock might, perhaps, be usefully distinguished in contradis- 

 tinction to Aggregates, or those formed of fragments. This great object 

 in experimental geology, I hope to accomplish by means of an instrument 

 which I have long had in use, for the regulation of high heats, a descrip- 

 tion of which may probably soon be laid before the Society, together with 

 some further results in support of the Huttonian Theory of the Earth."— 

 pp 15, 16. 



We again repeat our earnest solicitation to Sir James Hall 

 to make this invention known to the public. There is, we be- 

 lieve, at this moment, more than one chemist on the Conti- 

 nent,* if not in this country, engaged in the formation of crys- 

 tals in imitation of nature ; and as we know that the regula- 

 tion of high heats is by far the most difficult part of the pro- 

 cess, we trust that Sir James may be induced to lend the as- 

 sistance of this valuable instrument to a subject which, it 

 may be fairly presumed, he has as sincerely at heart as any man 

 in the field. 



Sir James Hall stands so high as an experimental geologist, 

 if we may be allowed the expression, and his authority is now 

 a-days so often quoted, that we think a reprint of all his pa- 

 pers, in a separate form, would be gratefully received by the 

 scientific world. 



Art. II. — On some Phenomena of Vertical and of La- 

 teral Mirage, observed at King George's Bastion, Leith. 

 An Extract of a Letter to the Editor, from Henry Home 

 Blackadder, Esq. Surgeon, Med. Staff", H. P. 



Close along the seashore, to the north-east of the new Hocks 

 at Leith, there is an extensive bulwark, the central part of 

 which is named King George's Bastion. This bulwark is 



" See this Journal, vol. i. p. 375, and vol. ii. p. 129. 



