Royal Ins f hut ion. 135 



tains half as nmch alkali as the second : also Dr. VVollas- 

 ton's experiment of equal weights of carbonate of potash, 

 one fii'-ed, the other in its common stale; the one contain- 

 ing exactly half as nnich gas as the olher. He said it was 

 in c()nse(|nence of these circumstances, that whenever com- 

 pounds decompose each other by double alHnity or double 

 attraction, there is always nierclv anew arrangement of their 

 elements, and none of the substances are found either in 

 excess or deficiency : he instanced the salt called nitrate of 

 barytes, which, when mixed with an equal weight of that 

 called sulphate of potash, the potash unites to the nitric 

 acid, and the barvtes to the sulphuric acid, and the results 

 are neutral as before. It is, said Mr. Davy, in consequence 

 of this simple law, that whenever one bodv precipitates 

 another from its solution, the same quantity of one always 

 precipitates the same quantity of the other ; and hence the 

 different chemical elements may be expressed by numbers, 

 and all their combinaiions be represented bv the simple ad- 

 dition of those numbers. Some of those principles, said 

 he, may appear abstruse ; but if the proportions be consi- 

 dered as uniform parts, there can be no difficulty in under- 

 standing the doctrine. On this part of the science, said the 

 Professor, it is necessary to gain distinct ideas ; the doc- 

 trines of chemical affinity become the instruments for com- 

 paring the results of our experiments, and their deviation 

 from or coincidence with the law of proportion are the 

 tests of their accuracy or imperfection. These doctrines, 

 said he, are capable of beino; made the guides both to the 

 practical and piulosophical chemist ; they teach the artist 

 or manufacturer what proportions of substances are neces- 

 sary for his condjinations, and enable him to pursue new 

 principles with precision and certainty. 



Mr. Davy delivered his fourth Lecture on Saturdav Feb. 

 15lh. He considered and illustrated the principles of elec- 

 trical science, as developed by the various combinations of 

 human ingenuity, and exhibited in the phEenomena taking 

 place in the external world. 



When resin, glass, &c. are rubbed by woollen, thev first 

 attract, and after contact repel, liohi substances, bodies in 

 such a state aie said to be electrical. This property was first 

 observed in amber, called (lectron by the Greeks, from 

 which the term electricity is derived. 



In the iGih century, the researciies of Gilbert awakened 

 the attention of philosophers. He considered electricity 

 as exhibiting the attractive and repellent powers of matter. 

 'I he sagacity of Newlon pointed out these powers as pecu- 

 liar forces. 



I 4 Otto 



