~ 
1560 
fent alfo to Citizen Fourcroy by Guada- 
loupe, andi‘to Sir Joieph Banks, by the 
Trinidad, our dapiché 5 or the white oxy- 
gen caoutchoue, which exudes from the 
roots of a tree in the forefts of Pimichin, 
nm? the moit remote corner of the werld, 
fowards the fources of Rio Negro. 
At length, afc-r waiting three years, 
La Mecanique Celefie of Laplace is avriv- 
ed, (November r8a2 ;) 1 have fallen upon 
ft with: unbounded eagernefs. This book 
has encouraged me to continue my re- 
fearches on the tides of the atmofphere, on 
which I made feveral obfervations at Cu- 
mana inthe year r799- I have mention- 
ed them in a letter to Citrzen Lalande.— 
Godin knew fomething about them, with- 
eut poimting out a caufe. Mofciy, ma 
work on the maladies of the Tropics, . 
gays, that the barometer is at the maximum 
when the fun isin the meridian; but that 
is very falfe. ‘The maximum takes place 
at zr h. and at 11 h. ; the mimimum at ah. 
and at 15ah. The Moon does not feem 
to alter the epochs fo much as the quan- 
tity of elevations. FT am now obfrving 
principally the days of eppofition and 
conjunétion ; and as my barometer indi- 
eates the zoth part of a line, I doubt not 
but Citizen Laplace, whofe genius has 
conquered the tides of the fea, will alfo 
difcover the laws of the tides of the air, 
when F fhall have given him fome thou- 
fands of obfervations. 
See how firiking the phenomenon is : 
fa be 
24. November, ro h. morn. 27 5 75 
12 4.9 5 45 
2 2G 5 25 
eee ee ee 3 29 5 Io 
ar i ee ed a ena 
————__——- 5 30 5 10 
g.'8 5 65 
IO 30 5 &5 
I obferve the hygrometer and barome- 
ter atthe fame time. My barometer is 
Englifh. . 
I have gone too far. I wifhed to write 
my friend Pommard. I have no more 
time ; he loves me, hewili excufe me. 
I don’t go to the Philippines. I pafs 
by Acapulco, Mexico, Havannah, to Ev- 
rope. I hope toembrace you in Septen= 
ber or O&ober 1803, at Paris. I fhall be 
at Mexico in February ; in June at Ha- 
vannah. I think of nothing but of pre- 
ferving and publifhing my manufcripts.— 
How much do I long to be at Paris! 
Health and refpect, 
HUMBOLDT. 
Proceedings of Learned Societies. 
[Sept. 1, 
TRANSACTIONS OF THE ROYAL 
SOCIETY. 
MINERALOGY AND CHEMISTRY. 
SHE. fir article under thefe heads is an 
elaborate defeription. of the corun- 
dum ficne, and its varieties, commonly 
keown by the names of oriental roby, 
{apohire, &c. by the Count de Bournon. 
Tt appears that this fubftance has hitherto 
prefented itfeif to notice under two 
appearances, which differ fo much from - 
each other in the greater number of thofe 
charaéters which moft forcibly effect our 
fenles, particularly thofe which concern 
the organ of fight, that it is no matter of 
furprize to find that .mineralogilts, feel 
fome reluctance, at the idea of uniting 
fubitances which appear fo very difimilar. 
Under one of thefe appearances, in 
which it is known by the name of corun- 
dum, this fubfiance prefents itfelf either 
in fragments, or in cryftais of a pretty 
large fize, the turface of which is gene- 
rally duil and rough; their texture, 
which is very much lamellated, ts fhown 
to be fo by their fracture :—their colour 
is a dull whitifh, greenifh, and fometimes 
yellowith giey. " 
Under the other appearance, in which 
this fubftance is known by the names of 
fapphire, ruby, &c. it offers irfelf, on the 
contrary, in cryftals which are generaily 
of afmal! fize, and have a fmooth and 
brilliant furface. ‘Their tranfparency 1s 
often very great ; and it feldom happens 
that they are not femi-tranfparent in 2 
greater or lefs degree. Their colours are 
much more beautiful, more variegated, 
and more lively. 
It is known in India (its native coun- 
try,) under the name of Corundum, and 
as that name has been generally adopted 
in Europe ;, it is continued by the Count, 
who diftinguithes it by the terms perfec? and 
‘imperfec, according to the fates in which 
it prefents itfelf to our obfervation. 
In examining more clofely thefe ftones, 
we are informed that with regard to their 
colour it is various, and feems to depend 
very much on the place where it is found. 
The corundum of the Carnatic differs 
from that found in China and Ava ; and. 
that on the ceaft of Malabar. is different 
from ali ene others.. In the perfe@ corun- 
dum, found iw Pegu and Ccylon, the co-_ 
lours are more various and lively ;_ the red 
colour confiitutes the oriental ruby; the 
azure blue, the fapphire; the yellow, 
which is always more or lefs mixed with 
a reddifh tint, is called the oriental topaz ; 
the purple colour conftitutes the oriental 
; amethyft. 
