238 
tinue in motion until something stops it; 2. A body 
moving in any direction is not retarded by a force 
exerted at right angles to its direction. 
We will suppose the ring to be laid aside, since it 
serves only for holding the disk, and that the disk or 
wheel is cut away until only a narrow strip is left, 
like two arms extending in opposite directions from 
the axle: its form will then resemble a T-square, 
which will now be used to illustrate the actions of 
the gyroscope. 
Hold*the'stem of the square in the left hand, close 
to the end, and make the cross-piece vertical; hold 
the left hand still, and let the cross-piece move up or 
down: evidently it will describe part of a circle. If 
it is held so that the cross is just in front of a plumb- 
line, so that both can be viewed at once, it will be 
seen that the upper end of the cross moves away from 
the plumb to the right, while the lower moves away 
from it also, but to the left. If, while the left hand 
remained stationary, the cross had been allowed to 
drop freely, the top and bottom would evidently ac- 
quire a certain horizontal motion, one to the right, 
the other to the left. If, now, the T-square be quick- 
ly turned over, so that the top and bottom change 
places, this will not interfere with motion previously 
acquired: the bottom (which has now become the 
top) will continue to move to the left, while that 
which was the top will move to the right; and, as 
the motion continues (as in case of a pendulum), the 
ends of the cross are pushed back to where they were, 
and the instrument rises to its first position. 
This explains why the gyroscope, in apparent de- 
fiance of the law of gravity, remains, when supported 
only at one end, in a horizontal position. 
To understand why the instrument rotates around 
the central point, in a direction always the opposite 
of that of the top of the disk, the T-square is again 
brought into service. Hold it as before, and let it fall 
a few inches: as in the first experiment, the top, when 
the 'T goes down, gets a motion towards the right; 
but, before the instrument can be reversed, it must go 
half way, and point horizontally, instead of up and 
down. Evidently the motion which sends the upper 
end to the right will push the instrument (if the top 
was revolved towards the south) towards the north: 
hence the horizontal motion. 
The horizontal motion is slow in proportion as that 
of the disk is rapid, because of the movement of the 
arms of the T. If the T turns slowly, it has more 
time to give motion to the ends of the arms, and 
consequently they push it around faster. If the T 
turns very quickly, it falls a very short distance (has 
so little time): hence the ends of the arms get very 
little motion, and, of course, can impart but little. 
A quick motion of the disk, therefore, makes a slow 
horizontal movement, and a slow motion of the disk 
makes a quick horizontal movement. 
A careful consideration of the above will make it 
easy to see why the gyroscope ceases to maintain itself 
if the lateral (or horizontal) motion is stopped; for, in 
order to maintain itself, the motion imparted to the 
ends of the T-square, when vertical, must be expended 
in lifting: if spent in any other way, nothing is left 
SCIENCE. 
ne 
’ 
[Vou. III, No. 5 oh 
to overcome gravity. Now if, as the square falls, and — 
the T has become horizontal, some obstacle prevent 
its moving still farther to the right, its motion in this — 
direction would cease; and, of course, when it arrived _ 
at the lowest point, nothing would be left to lift the 
instrument. 
Another paradox is, that the instrument must fall 
somewhat, in order to produce any of its peculiar phe- 
nomena; but this, too, is easily explained. Every 
thing depends upon the two extremities of the T get- 
ting a motion, one to the right and the otherto the ~ 
left, when the T is vertical. If the T does not fall, 
or if it is not lifted up (for either movement will do 
equally well), there will be no such motion: only, if 
the first sends the instrument north, the other will 
send it south. 
This directly or impliedly explains all the phe- 
nomena of the gyroscope. | 
NOTES AND NEWS. 
THE death of Guyot has been soon followed by 
that of another of the notable scientific men, who, — 
educated in Europe, took up their lot with us, and — 
became, so to say, wholly our own. Dr. George Engel- — 
mann of St. Louis—our oldest botanist (excepting 
the venerable Lesquereux), as well as an eminent phy- 
sician, for a time a fellow-student with Agassiz in 
Germany — died on the 11th inst., at the age of sev- — 
enty-five. A biographical notice may be expected in 
an ensuing number. 
—The Journal of agricultural science proposed 
from the North Carolina agricultural station recently, 
and to which we referred Dec. 28, has met with uni- 
versal approval and most unexpected support. 
Nearly one hundred shares of stock have been taken 
upon the plan proposed; and the Houghton farm: 
proposes to assume all of the mechanical work of a ~ 
monthly journal, and guarantee this part of its ex- — 
pense for one year. Without any special effort to 
secure them, about three hundred subscribers are 4 
reported. 
In response to a cordial invitation of the commis- 
sioner of agriculture, a meeting will be held to organ- 
ize this enterprise, at the Department of agriculture 
at Washington, at ten A.M., Wednesday, Feb. 27. All 
the friends of the scheme are urged to be present at 
this meeting, and participate in the inauguration of — 
the journal. It is hoped that each agricultural col- — 
lege, experiment-station, etc., will send a representa~ — 
tive. 
— Commodore Samuel R. Franklin, U.S.N., has — 
been detached from duty on the naval examining 
board, and ordered as superintendent of the naval 
observatory, to succeed Rear-Admiral R. W. Shufeldt, 
who was placed upon the retired list on Feb. 21. — 
— At a concert given by the Choral club of the Uni- 
versity of Wisconsin on the evening of Feb. 8, two 
songs by Sir William Herschel were sung, — the first, 
a glee, ‘Go, gentle breezes;’ the second, a catch, 
