A Question respecting the Strength of Oak and Fiu 391 



corked and uncorked phials, afterwards a solid crust has formed 

 in the upper part of the phials, without any obvious cause. Dr. C. 

 considers it the most singular and inex])licable fact, that when 

 regular, firm, transparent crystals are deposited (under all the 

 above circumstances), as soon as the remaining saturated solution 

 above tliem consolidates, the first formed crystals almost instantly 

 lose their transparency, and become of a porcelain white colour. 

 He ascribes this change to the abstraction of water of crystalli- 

 zation, as he found that the whitish mass, w^hen dissolved in wa- 

 ter and again crvstallized, afforded a quantity of transparent 

 crystals heavier than the original white ones. In this and in all 

 the other experiments Dr. Coxe has taken no notice of the ac- 

 tion of light, nor does he appear to be aware that light has a 

 potent influence on crystallization. Dr. Brewster's ingenious 

 and successful experiments on the effects of saline solutions on 

 rays of light, prove the necessity of attending to their influence 

 in all experiments of this kind. Dr. C. has ti'ied similar experi- 

 ments with solutions of alum, sulphates of magnesia, iron, cop- 

 per, and zinc, muriate of lime and subcarbonate of soda, with- 

 out any very notable dissimilaritv. But so uncertain and irre- 

 gular were the results, that in no case could he anticipate them. 

 He thinks, indeed, that his experiments fully disprove the theory 

 of latent heat, which iias itself become latent long ago, as water 

 saturated at 212" remained fluid and transparent even at the 

 freezing point, although the theory ascribes its solvent power to 

 the temperature. 



A QUESTION RESPECTING THE COMPARATIVE STRENGTH OF 

 OAK AND FIR. 



To Mr. Tillock. 



Sir, — In most of the authors who have written on the strength 

 of materials, we meet with the following assertion, viz. " Oak 

 will suspend much more than fir, but fir will support twice as 

 much as oak." As it is of some importance to the practical 

 mechanic to know how far this statement may be depended 

 upon, I would thank any of your correspondents to inform me, 

 if the above assertion rests on any better authority than that of 

 Muschenbrock's experiments with pieces four feet long and 

 7-lOths of an inch square ? For it would be easy to show that 

 the repulsive force of oak, or of any other material, could not 

 be ascertained by these experiments. 



I have tried several experiments on both kinds of timber, and 

 find that oak will both suspend and support more than fir, the 

 specimens being equally good of their kinds. 



In making the new experiments, at Woolwich, an attempt 

 B b 4 might 



