186 Mr. Kemp’s Experiments on Galvanism. 
a chemical action, the needle was strongly affected, although no 
oxygen was present to combine with the sulphur. tae 3 
In this experiment we have electricity generated apparently by 
the combination of a simple substance with the metals, which is 
somewhat at variance with the chemical theory that supposes a 
compound body to be necessary to produce this action. | 
_ I am inclined to suppose that all substances, conductors or non- 
conductors of electricity, whether they be simple or compound, 
provided they are brought toa liquid state, and are capable of 
combining with one of the metals used, will be also found to trans- 
mit that electricity which they may have generated by the chemi- 
eal action on the plate. 9 
These simple galvanic arrangements can be increased so as to 
form batteries, and their effects more decisively ascertained. 

SCIENTIFIC REVIEWS. 
Travels in the Interior of Mexico, in 1825, 26, 27, and 28. By 
Lizut. W. H. Harpy, R.N. Colburn. London, 1820. 
_ WE are indebted for these travels to “ the General Pearl and 
Coral Fishery Association of London,” which, in the year 1825, 
commissioned Mr. Hardy to- establish a pearl fishery in the Gulf of 
California, and which, after numerous dithculties put in his way 
both by the general and local authorities, and only with the use of 
much diplomatic talent, he succeeded in accomplishing, though 
finally without any success. Many circumstances connected with 
the local character of the waters, appear to contribute towards a 
tendency to the formation of pearls in the shells of certain mollus. 
cous animals ; but with respect to the animal itself, nothing ap- 
pears more intimately connected with their formation, than its age 
and undisturbed possession, in oysters, of rocky and sheltered gulfs 
or bays ; or in fresh water mussels, of mountain streams coursing 
into deep and tranquil lakes. Under these circumstances, they - 
do not lie in beds heaped one upon another, as when art has fos- 
tered the breed, but adhere singly aud firmly to the ruck, in chasms 
and sheltered cavities; and notwithstanding the failure of the 
means employed by Mr. Hardy, we are still inclined to think with 
Baron Humboldt, that the pearl fishery of these districts will one 
day become an object of very high importance. 
_ The interest of Mr. Hardy’s journey lies principally in his navi- 
gation of the Gulf of California and the Rio Colorado, and in his 
travels in unfrequented parts of Sonora. A good describer of cha- 
racter and of national manners, his work abounds in lively portraits 
and scenes, strongly characteristic of a nation surrounded by sources 
