Intelligence and Miscellayieoiis Articles. 229 



iih The subject is further elucidated by the application of the remark- 

 able symbol e*'^~^, a symbol which in geometry serves to indicate 

 the direction in which a line is drawn with respect to a given fixed 

 line ; the same symbol is perfectly applicable as a sign of aiFection 

 for forces, and hence the conclusion is strengthened that the ground 

 df truth in the two sciences is the same. 



'" The reasoning of this paper extends not only to forces, but also 

 to velocities and moments, and to all expressions of whatever kind 

 of the pure ideas of magnitude and direction, 



"If the author's reasoning be sound, the elementary propositions of 

 riifechanics are necessary truths in as strict, in fact, in exactly the 

 same, sense as the elementary propositions of geometry ; and to a 

 mind which dwells upon them, the truths of the one science ought 

 to appear in as axiomatic a light as those of the other. 



XXXIV. Intelligence and Miscellaneous Articles. 



ADDITIONAL NOTE TO MR. SULLIVAN's PAPER AT p. 161 OF 

 THE PRESENT NUMBER. 



CINCE writing the preceding paper, a short notice on the 

 ^ same subject has been published by Prof. Kersten*, in 

 which he speaks of having detected chlorine in a specimen of 

 lava from Niedermennig. I am glad that 1 can add a few ex- 

 periments on the same point. In nearly all the basalts, clink- 

 stone, one specimen of granite, diorite, and particularly car- 

 boniferous slate, from which I never found it absent, I could 

 detect chlorine by the same means as that employed by Ker- 

 sten. Fluorine appears to be equally diffused, as I could de- 

 tect its presence in nearly all the minerals which I analysed, 

 but particularly in diorite from the Lahn, and the carbonife- 

 rous slate from the south of Ireland. The following is the 

 method which I adopted for the detection of the fluorine, par- 

 ticularly in bodies undecomposable by means of sulphuric 

 acid, recommended by Rose. The mineral, finely pulverised, 

 was ignited in a platinum crucible with from three to four 

 times its weight of carbonate of soda; the ignited mass moist- 

 ened with water, and the soluble portion filtered from the in- 

 soluble. Care should be taken to employ as little water as 

 possible. The solution thus obtained is to be poured into a 

 platinum capsule, and very carefully supersaturated with hy- 

 drochloric acid. In stirring the solution no glass should be 

 employed, but either platinum or silver. The acid should be 

 allowed to rest for some time until all the carbonic acid has 

 escaped. When no more is evolved, the liquor should be su- 

 persaturated with ammonia, and the whole poured into a flask 

 provided with a cork. Chloride of calcium is then to be 

 * Page 155 of the present volume. 



