12 Proposal of another Number as 



solubility is the greatest; and that in the process of evapora- 

 tion, the dried salt is not presented to us in that state of ar- 

 rangement in which it previously existed in the fluid mass; and 

 thus in many instances what we conclude to be the chloride 

 of sodium is the chloride of calcium. 



In the year 1825, Mons, Peschier of Geneva published 

 some interesting researches on titanium: he has discovered it 

 as existing in considerable proportions in mica, talc, chlorite, 

 steatite, asbestus, marl, and eisspath. The results induced me 

 to examine the Mona marble of Anglesea. Although I have 

 detected titanium [?], as soon as my series of experiments are 

 concluded, I shall have great pleasure in transmitting them to 

 the public through the medium of your valuable Journal. 



I am, Gentlemen, yours respectfully, 

 Ambleside, Cumberland, Nov. 8, 1829. R. HENDERSON, M.D. 



IV. Proposal of another Number as a Test of the Chronometers 

 071 Trial at Gi-eenmch. By J. L. T. 



T^HE observations of Caleb Mainspring in the last Number 

 -*■ of the Philosophical Magazine, on the trial number hitherto 

 applied for awarding the prizes for the best chronometers, have 

 induced me to propose another number to be substituted for 

 it; the application of which, although certainly more laborious 

 than that of the former one, would be by no means very diffi- 

 cult, especially after a little practice. C. M.'s remarks prove 

 that the present trial number is not an absolute test of the 

 quality of a chronometer; it is, indeed, clear from the deriva- 

 tion of the number, that almost every day's differences might 

 undergo slight alterations, the accumulated sums of which 

 would be considerable, without altering that number. The 

 object which the Admiralty must have in view, is to find out 

 those chronometers which will most exactly retain the rates 

 derived from a certain, longer or shorter, interval, during an 

 uncertain subsequent period. The usual and most important 

 application of chronometers for determining the longitude at 

 sea, by means of a rate, previously determined in port or on 

 shore, does not admit of any regard to the alterations, how- 

 ever regular to all appearance, of that rate which in other ap- 

 plications of chronometers might be admitted and taken into 

 account. The Admiralty can, therefore, not look to any other 

 differences but the first, and should award the prizes to those 

 chronometers only, which present the greatest uniformity in 

 the first differences of their daily differences from the mean 



time 



