ELA 
B at rest, weighing also two ounces, the 
body B will move forward after the stroke 
with the velocity 16, A remaining at rest in 
its place. The reason of this is, that the 
body A loses one half of its motion by 
striking the equal body B, and the other 
half by the elasticity of B, recovering its 
former figure. From this experiment, se- 
veral curious phenomena arise : thus, if 
a row of shovel-board pieces (that is, metal- 
line cylinders of about half an inch in height, 
and two inches diameter) be laid upon a 
smooth table, and you take a single piece, 
and drive it against the row, the last piece 
of the row will fly offj for ifA(fig. 11.) strike 
the row of pieces B, C, D, E, F, G, H, I, 
in tlie direction A a, then will the last piece 
I fly off to i with the same velocity that A 
stnick B : and whatever be the velocity of 
A, no other piece but the last piece I will 
fly off. But if you take two pieces, as A 
and B, (fig. 12.) and strike them together 
against the row C, D, E, F, G, H, I, the 
two last pieces, H and I, will fly off from 
the other end of the row with the same 
velocity that A and B made the stroke. 
If three or mote pieces are made use of 
to make the stroke, the very same number 
will fly off" from the other end of the row ; 
and, it is to be observed, that the same will 
happen with equal elastic balls, suspended 
in a row by strings of the same length. 
Again, if the elastic body A, (fig. 13.) 
weighing four ounces, strike the quiescent 
body B, weighing only two ounces, with a 
velocity equal to 12 ; then will the velocity 
of A, after the stroke, be 4, and that of B 
16. Just the reverse of this happens when 
a lesser body strikes against the greater; in 
which case, the striking, or lesser body, will 
be reflected with one-fourth of its first mo- 
tion, and the greater be carried forward 
with a motion which is as 16. 
The magnitude and motions of spherical 
bodies perfectly elastic, and moving in the 
same right line, and meeting each other, 
being given, their motion after reflection 
may be determined thus: let the bodies be 
called A and B, and the respective velocities 
a and b ; then, if the bodies tend the same 
way, and A, moving swifter than B, follows 
it, the velocity of the body A, after the re- 
flection, will be and that 
of the body B = — 6A-j-6B 
if the bodies meet, then changing the sine of 
h, the velocity of A will be 
ELA 
jii I 2aA-|-&A — feB , 
and tliat of B = ; and if 
A Jd 
either of these happen to come out nega- 
tive, the motion after the stroke tends the 
contrary way to that of A before it ; wliich 
is also to be understood of the motion of- 
the body A in the first case. 
ELATE, in botany, a genus of the 
Apendix Palm®. Natural order of Palms. 
Essential character : male, calyx three- 
toothed ; corolla three-petalled ; anthers six, 
sessile. Female, calyx one-leafed ; corolla 
three-petalled ; pistils one ; stigmas three ; 
drupe one-seeded. There is but one spe- 
cies, viz. E. sylvestris, prickly leaved elate. 
This palm grows to the height of fourteen 
feet, covered with an ash-coloured crust, 
closely united with a hard whitish wood ; 
pinnate leaves break out from the top of 
the trunk only, in a decussated order ; the 
old ones dropping off as the young ones 
break forth. The flowers are concealed in 
stiff, green, coriaceous spathes, tliey are 
small, several on the same peduncle ; petals 
whitish green ; they have no smell, but a 
rough taste. The fruit is like a wild plum, 
with a hard woody point at top, covered 
with the calyx at bottom. The nut or stone 
is oblong, marked longitudinally with a 
deep furrow, containing a bitter kernel. 
The poorer sort of people chew the nut in 
the same manner as the areca nut, with the 
leaf of the betel and quicklime. Tlie ele- 
phants are very fond of the fruit branches, 
which are sweet. It is a native of the East 
Indies. 
ELATER, in natural history, a genus of 
insects of the order Coleoptera : antenn® 
filiform, lodged in a groove under the head 
and thorax : underside of the thorax termi- 
nating in an elastic spine, placed in a cavity 
of the abdomen ; by which means the 
body, when placed on the back, springs up 
and recovers its natural posture. This ge- 
nus, which is extremely numerous, is di- 
vided into two sections, viz. A. feelers 
hatchet-shaped ; and B. feelers clavate, the 
club round. Of the latter only three spe- 
cies are mentioned, but of the former two 
hundred at least have been enumerated. In 
point of size the European species are not 
comparable to those which are natives of 
the tropical regions. Among the most re- 
markable may be mentioned E. flabellicor- 
nis, which is more than two inches long, 
and is a native of India, and of many parts of 
Africa. E. noctilucus, found in South 
America, and called there coenjas, is not so 
large as the last, but the spots on tiie tho- 
9 
