BRITISH ASSOCIATION. 51 



there are greatly different departures, that is to say, of three millimetres, or when 

 there is change of inclination, there must be sent a message at noon or in the eve- 

 nino' of the same day. In all cases, not only the pressure in the morning, but 

 likewise that at night should be given. A critical indication is, when the previous 

 day the northern stations had greater departures, and the following day the south- 

 ern had greater departures, even when the difference iu the latter case was small. 

 There is caution to be had when the difference of the departures is 4 millimetres. 

 But I may not trespass on your time and kindness in expressing wishes only, it 

 may be sufficient to have communicated the general rule. 



* On Aluminium,' by Mr. I. L. Bell. — The author said — " The progress of the 

 manufacture of this, so far as the arts are concerned, new metal has scarcely been 

 Buch as to require much to be added to the researches bestowed upon the process 

 by the distinguished chemist, M. St. Cairi Deville, of Paris. Upon the introduc- 

 tion of its manufacture at Washington, three years and a half ago, the source of 

 the alumina was the ordinary ammonia alum of commerce, a nearly pure sulphate 

 of alumina and ammonia. Exposure to heat drove off the water, sulphuric acid 

 and ammonia, leaving the alumina. This was converted into the donbie chloride 

 of aluminium and sodium by the process described by the French chemist and 

 practised in France, and the double chloride subsequently decomposed by fusion 

 with sodium. Faint, however, as the traces might be of impurity in the alum it- 

 self, they, to a great extent, if not entirely, being of a fixed character when exposed 

 to heat, were to be found in the alumina, from which, by the action of the chlor- 

 ine on the heated mass, a large proportion, if not all, found their way into the 

 sublimed double chloride, and once there, it is uuneeessary to say that under the 

 influence of the sodium, any silica, iron, or phosphorus found their way into the 

 aluminium sought to be obtained. Now, it happens that the presence of these im- 

 purities in a degree so small as almost to be infinitesimal, interferes so largely 

 with the colour as well as with the malleability of the aluminium that the use of 

 any substance containing them is of a fatal character. Nor is this ail, for (he na- 

 ture of that compound which hitherto has constituted the most important appli- 

 cation to this metal — I mean aluminium-bronze — is so completely changed by 

 using aluminium containing the impurities referred to, that itceases to possess any 

 of those properties which render it valuable. As an example of the amount of in- 

 terference exercised by very minute quantities of foreign matters, it is, perhaps, 

 worthy of notice that very few varieties of copper have been found susceptible of 

 being employed for the manufacture of aluminium-bronze ; and hitherto we have 

 not at Washington, nor have they in France, been able to establish in what the 

 difference consists between copper fit for the production of aluminium-bronze, and 

 that which is utterly unsuitable for the purpose. These considerations have led 

 us, both here and in France, to adopt the use of another raw material for the pro- 

 duction of aluminium, which either does not contain the impurities referred to as 

 BO prejudicial, or contains them in such a form as to admit of their easy separa- 

 tion. This material is Bauxite, so called from the name of the locality where it 

 is found in France. The Bauxite is ground and mixed with tke ordinary alkali of 

 commerce, heated in a furnace. The metal is so extensively used in the arts as 

 to keep the only work in England, namely, that at Washington, pretty actively 

 employed. As a substance for works of art, when whitened by means of hydro- 



