280 Notice of Delafosse 's Memoir on Crystallography. 



deal depends on the flame of the volatile matter. If, however, 

 any reliance is to he placed in the experiments the results of 

 which I have detailed, I think they will be forced to allow that 

 ' I am correct in what I assert : that the greater the proportion 

 of fixed carbon in a fuel, the greater will be the practical eva- 

 porative power. In a national point of view, then, now that 

 the demand for fuel has become so great, and that for long 

 voyages it is of the utmost consequence to have the fuel power- 

 ful, so as to occupy as little space as possible, or rather, if 

 I may be allowed the expression, to have a greater quantity 

 of an evaporative power stowed away in the same space, it is 

 of vast importance that attempts should be made to introduce 

 the anthracite fuel. 



Notice of Delafosse' 's Memoir on Crystallography* 



It is known that when we compare the physical characters 

 of the forms which compose the different systems of crystal- 

 lization with their proper geometrical characters, we arrive at 

 the following general fact : that, in a crystal, all the parts of 

 the same geometrical species are modified at once and in the 

 same manner, or, reciprocally, that the parts of different 

 geometrical species are modified individually or differently. 

 We meet, however, with certain bodies in which the mo- 

 difications take place differently than in others, insomuch 

 that all the parts geometrically alike are no longer found to 

 be modified in the same manner. Now, says M. Beudant, 

 it has happened with regard to this observation, what we too 

 often witness in the sciences — observers have seen only one 

 possible conclusion, without suspecting that another may exist 

 quite as admissible. It has been simply concluded, in this 

 instance, that these circumstances constituted an exception 

 to the law of symmetry ; and trusting implicitly to the adage, 



* At a meeting of the Academy of Sciences of Paris on the 25th January 

 1841, M. Beudant read a report, drawn up conjointly by MM. Brongniart 

 and Cordior, on a crystallographical memoir presented by M. Delafosse, of 

 which the above is a notice. 



