424 
lour moft favourable to the reflection of 
calorific and frigorific rays, it muft be ac- 
knowledged that thefe animals have been 
exceedingly fortunate, in obtaining cloth- 
ing fo wel] adapted to their local circum- 
ftances. 
The exceflive cold which reigns on the 
tops of very high mountains, and in the 
higher regions of the atmofphere; and 
the frofts at night, which fo frequently 
take place on the furface of the plains be- 
low, in very clear and ftill weather, feem 
to indicate that frigorific rays arrive con- 
tinually at the furface of the earth from 
every part of the heavens. May it not 
be by the action of thefe rays that-our 
planet is cool continually, and enabled to 
preferve the fame mean temperature for 
ages, notwithftanding the immenfe quan- 
tities of heat that are generated at its fur-" 
face, by the continual ation of the folar 
rays? If this conjeéture thould be well 
founded, we fhould be led to conclude 
that the inhabitants of certain hot coun- 
tries, who fleep at night on the tops of 
their houfes, in order to be more cool and 
comfortable, do wifely in choofing that 
fituation to pals their hours of reft. 
Mr. KnicuT ha’ communicated to the 
Royal Society an account of fome farther 
experiments and obfervations on the mo- 
tion of the fap in trees. Ina former pa- 
per, he offered a conjeSure, that the vef- 
fels of the bark which pafs from the 
leaves to the extremities of the roots, 
were, in their organization, better calcu- 
lated to carry the fluids they contain to- 
wards the roots than in an oppofite di- 
rection, becaufe the forms generally af- 
fumed by trees, in their growth, evince 
the compound and contending aétions of 
gravitation, and of an intrinfic power in 
the veflels of the bark, to give motion to 
the fluid pafling through them. In the 
experiments now detailed, the cuttings of 
feveral kinds of trees have been planted 
3n the natural pofition, and alfo inverted, 
in fome, thofe which were inverted did 
not ftrike root: in othess, as in the falix 
caprea, or fallow, the whole, both thofe 
inverted and thofe in their natural pcfi- 
tion, emitted roots, and grew with luxu- 
riance ; but their modes cf growth were 
extremely different. In the cuttings 
which food in their natural pofition, ve- 
getation proceeded with moft vigour at 
the points moft elevated ; but in the in- 
Proceedings of Learned Societies. 
S [ Dec. ly 
verted cuttings, if grew more and more 
languid, as it became diftant from the 
ground, and nearly ceafid towards the 
conclufion of the fummer. 
From thefe and ether taéis, Mr. Knight 
thinks that the veffeis of plants are not 
equally well calculated to carry their 
contents in oppofite directions, and that 
the veffels of the bark, like thofe which 
conftitute the venous fytem of animals, 
to which, in many refpeéts, they are ana- 
Jogous, may be provided with valves, 
whofe extreme minutenefs has concealed 
them from obfervation. : 
Dr. Russev has laid before this learned 
body fome oofervations on the orifices 
found in certain poifon-fnakes,’ fituaied 
between the noftril ard the eye, with re- 
marks by Mr. Everard Home. The Caunt 
de la Cepede, who notices thefe orifices 
in the yellow fnake of Martinico,” fays 
that fome naturalifts conceived them to 
be the organs of hearing; but Dr. Ruf. 
fel informs us that Mr. Home’s inveftiga- 
tions have clearly eftablifhed, that the la- 
teral orifices in ferpents, and the bags to 
which they lead, have no communication 
with the organ of hearing. And Mr, 
Home himfelf fays that the fats which 
were reported to the Society were fuffi- 
cient to prove that the bags have a fecre- 
tion of their own, the quantity of which 
varies, according to the climate, and other 
circumitances: and as amphibious ani- 
mals in general have no glands to fupply 
the fkin with moiftere from within, but 
receive it by coming in contaét with 
moift fubftances, it is. poffible the bags, 
in the {nake, may be fupplied in that man- | 
ner, and the more fo, as the cuticular lia- 
ing appears perfect. : 
Another peculiarity is remarkable in 
fnakes furnifhed with thefe bags, namely, 
an oval cavity, fituated between the bag 
and the eye, the opening into which is 
within the inner angle ct the eyelid, and 
dire&ted towards the cornea. In this 
opening there-are two rows of projection, 
which appear to form an orifice, capable 
of dilatation and contraétion. From the 
fituation of thefe oval cavities, they muf 
he confidered as rcfervoirs for a fluid, 
which is occafionally to. be {pread over 
the cornea ; and they may he filled by the 
failing of the dew, or the moifture fhaken— 
off from the gtafs through which the fhake. 
pafles.-  - . : 
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