340 
POPULAR SCIENCE REVIEW. 
2nd. The so called non-magnetic metals have all quotients above 4. There 
is, however, one exception to this rule, in the case of copper, of which the 
respective specific and atomic weights are 8*8 and 31-7, of which the quotient 
is 3-602 : hut then it is probable that the atomic weight of copper needs 
correction, and should be doubled to 63-4, in which case the quotient would 
be 7-204, and it would then fall among the other non-magnetic metals. 
3rd. The quotients are the smallest for those metals which are the most 
permanently magnetic, even at high temperature, and vice vei'sd. 
Polar Magnetism . — An essay on Polar Magnetism was recently read 
before the American Institute, and has been reprinted by the author, Mr. 
John S. Parker, who has favoured us with a copy. This pamphlet is a very 
clear exposition of a very difficult subject. Mr. Parker thinks that the 
cause of the variations of the compass, which some have attributed to the 
oscillation of the earth, is really due to the revolution of the magnetic pole 
around the North Pole, a revolution which is generally completed in about 
six hundred and forty years. There is one point in Mr. Parker’s paper to 
which we would make exception, and that is his attempt to explain gravity. 
This is trying too far. 
ZOOLOGY AND COMPARATTV^E ANATOMY. 
The Salivary Apparatus in Edentata. — M. G . Pouchet laid a memoir on 
this subject before the French Academy, at its sitting on March 30 last. 
The general conclusion which his researches would appear to warrant is that 
in these animals the salivary glands are more complex than usual, and that 
the pouring out of the saliva is not involuntary, but is directly imder the 
control of the animal’s wiU. The excretory ducts of the salivary glands of 
Edentata are, he states, very large, and are two in number, for each gland. 
In some of the genera the duct expands into a capacious sac. This sac is 
lined with a layer of voluntary muscles. The fibres arise from those of the 
mylo-hyoid muscle, and are arranged spirally, something like those seen in 
the heart. There are also valves which, when the sac contracts, prevents 
the regurgitation of the liquid towards the gland. In the ant-eaters, how- 
ever, this arrangement is absent. The excretory ducts are certainly con- 
siderably dilated, but there are no valves, and the secretion is discharged 
through the combined action of the mylo-hyoid muscle and the tongue. 
Are there Two species of Horse ? — The researches which M. Sanson has 
lately carried out, and which are published in part in the Comptes Rendus^ 
Tome LXVI., No. 137, have led him to the folio wing, important conclu- 
sions : — (1) There are in the East two specific types of horse, which have 
hitherto been confounded under the single name of Arab. (2) These are at 
once distinguished by their craniological character, and by the number of 
their vertebrae, as well as by other peculiarities. (3) They are both Brachy- 
cephalic, but in one the frontal is flat, the nasal bones are rectilinear, and 
there are d.r lumbar, seven cervical, eighteen dorsal, and five sacral ver- 
tebrae; the other has the frontal convex, the true nasal bones slightly 
curvilinear, and has only Jive lumbar vertebrae, the remaining vertebrae 
