TON 
gular but conspicuous foraminas into the 
mouth. See Anatomy. 
TONTINE, a variable kind of life an- 
nuity, but generally so contrived as to be 
progressively increasing in amount. It is 
formed by nominating a certain number of 
lives. within limited ages, who for each one 
hundred pounds, or any other gross sura 
paid down, are to receive at first a specific 
annuity, but as any of the lives fail, their 
annuity is to be equally divided among 
those that remain, by which mfeans those 
who happen to survive a considerable num- 
ber of years, obtain a large augmentation 
of their annual receipt, and the life, which 
is the longest liver of the whole (if there is 
no restriction to the contrary) gets for the 
remainder of its continuance, the total 
sum paid at first to all the nominees. Ton- 
tines of this kind, if properly conducted, 
are considered by some persons as afford- 
ing an eligible opportunity of making some 
provision for children, as the nomination of 
young healthy lives gives a good chance of 
survivorship. It has several times been 
attempted to raise money on this species of 
annuity for the service of government, but 
it has never been found practicable to ob- 
tain any considerable sum in this way ; on 
a smaller scale it has been adopted success- 
fully both in Great Britain and Ireland, for 
procuring the sums necessary for building 
bridges, large inns or hotels, and other ex- 
pensive edifices. 
Of late years many delusive schemes 
Lave been set on foot under the name of 
tontines, but differing very materially from 
the plan above mentioned, as they do not 
require a gross sum to be paid down, but 
quarterly or half yearly payments during 
their continuance, which is limited to the 
short period of five, seven, or ten years ; 
the intention being, that the subscribers 
should receive back all they had contri- 
buted, with the additions made to it from 
improvement at compound interest, and 
the division of the contributions of such as 
might happen to die within the term. But 
the difference between compound and sim- 
ple interest in the improvement of such 
payments, for a short time, is so trifling, 
and the probability of any .considerable re- 
duction, during such term, in the number 
of a set of young lives, who it may be pre- 
sumed were thought healthy subjects at the 
time of their nomination, is so small, that 
the advantages derived from these sources 
have been sometimes overbalanced by the 
expenses of management, and, in fact, in 
TOP 
several instances of these schemes, which 
have expired within these few years past 
the subscribers have actually received con- 
siderably less than the payments they had 
made would have amounted to without any 
improvement at interest. 
TOP, in naval affairs, a sort of platform 
surrounding the lower mast head, from 
which it projects on all sides like a scaffold. 
The intention of the top is to extend the 
top-mast shrouds so as to form a greater 
angle with the mast, and thereby give addi- 
tional support to the latter. The top is 
likewise convenient to contain the mate- 
rials necessary for extending the small sails, 
and for fixing and repairing the rigging and 
machinery with greater expedition. In 
ships of war, the tops are furnished with 
swivels, musketry, and other fire-arms, and 
are guarded with a fence of hammocks in 
time ot action. In this case the top is used 
as a kind of redoubt ; and is accordingly 
fortified for attack or defence, being fur- 
nished w'ith arms, and guarded by a thick 
fence of corded hammocks. The top is 
employed likewise as a place for looking- 
out, either in the ,day or night. 
TOPAZ, in mineralogy, fs a species of 
the flint genus, of a wine-yellow colour, of 
all degrees of intensity, and passing to va- 
rious other colours. It occurs massive, dis- 
seminated, sometimes in rolled pieces, but 
commonly crystallized. There are many 
varieties. Specific gravity, according to 
Werner, is about 3.5. The Saxon variety-, 
in a gentle heat, turns white ; but a strong 
heat deprives it of lustre and transparency : 
the Brazilian, by exposure to a high tem- 
perature, burns rose-red; and in a still 
higher, violet-blue. Before the blow-pipe 
it is scarcely fusible; but exposed to a 
stream of oxygen gas, it melts into a por- 
cellanous bead. It is fusible with borax, 
but alkali has little effect on it. The Bra- 
zilian, Siberian, and other topazes, when 
heated, exhibit at one extremity positive, 
and at the other negative electricity. The 
Saxon topaz, by friction only, gives signs 
of electricity. The constituent parts are, 
according to Vauquelin, 
Silica 
Alumina gg 
Loss T 
100 
It is found in veins that traverse primi- 
tive rocks, accompanied by fluor-spar, tin 
ore, and arsenical pyrites. It is found in 
Brazil ; in Siberia, among the Uralian moun- 
