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TO OUR READERS AND CORRESPONDENTS.
A Correspondent at Glasgow (whose letter has been mislaid) informs us that Dr. HALL has been anticipated in his views respecting the cause of vomiting, by Richerand, to whose work on Physiology we are referred.
We are sorry that a notice of an ingenious little Essay on Bridges, illustrated by Models, does not come within the scope of this Journal. We allude to the publication of Essex and Co.
We have not received a promised Communication from our Correspondent at Chatham.
The Tables attached to Mr. S.'s paper are far too voluminous.
We find nothing sufficiently new in the paper on Toadstone to induce us to publish it.
The Report to the African Association reached us too late for notice.
It is with sincere and deep regret that we announce the death of Dr. THOMAS YOUNG, which took place at his house in Park Square, in the early part of June.
We have also the painful duty of recording the death of Sir HUMPHRY DAVY, which occurred at Geneva, after protracted illness, on the 20th of May.
Thus, within the short period of six months, the scientific world has lost three of its most distinguished members,
WOLLASTON, YOUNG, and DAVY.
SCIENCE, LITERATURE, AND ART.
An Account of M. BESSEL'S Pendulum Experiments. THE Volume of the transactions of the Berlin Academy which is just published contains the very important memoir of M. Bessel on the length of the seconds pendulum at Königsberg.
Having had an opportunity, in the summer of last year, for which I am greatly obliged to Professor Schumacher, of examining M. Bessel's apparatus, set up for that purpose in the observatory at Hamburgh, with the advantage of the presence of the eminent artist, M. Repsold, by whom it was made, and furnished with M. Bessel's memoir then unpublished, I trust that the following early notice of its valuable contents may not prove unacceptable to those who in this country are interested in the same pursuit, and are still awaiting the arrival of their long expected copies. To such it will not supersede the perusal of the work itself, abounding as it does in original and profound discussion, on a subject which has numbered, and still numbers, amongst those who are engaged in it, the most distinguished names of continental science. To more general scientific readers, it will convey some knowledge of an important work, of which probably not more than a few copies will be in circulation in this country, and those in a language (the German) which is not so generally read amongst us as it deserves to be, although becoming more so every day.
M. Bessel's memoir may be divided into two general heads : first, the measurement of the seconds pendulum at Königsberg, by a new method, invented by himself; and, second, dissertations and experiments on points connected with pendulum experiments generally.
The principle of M. Bessel's method of determining the seconds pendulum bears a near resemblance to that of our ingenious countrymen, and early experimentalists in pendulums, Hatton and Whitehurst. It consists in the application of a moveable point of suspension to a pendulum, composed of a brass ball and metallic thread. The brass ball remains always at the same level, and the metallic thread is shorter or longer according as the suspension is brought nearer or removed further from the ball. The effect is thus produced of two pendulums, of which the difference in length is known, being the interval between the points of suspension in the two cases; the interval being made, mechanically, equal to the distance comprised between the extremities of a standard bar. The ratio of their lengths is also known, by observing the number of vibrations performed by each in a given time. Whence the time of vibration due to the length comprised between the points of suspension in the two cases, i. e. to the length of the standard bar, is obtained; and the length of the seconds pendulum is finally deduced.
This method has two advantages which entitle it to great consideration it avoids the difficult and very delicate operation, of comparing a definite length on the experimental pendulum with a standard scale; and the result is independent of what may be the exact situation of the axis of motion in the suspension of the pendulum of experiment.
The apparatus and processes by which the principle adopted by M. Bessel is carried into effect, are, we believe, entirely new, as well as original, and highly ingenious. The apparatus consists of a vertical bar of iron, ten feet long by four inches broad, and four lines thick, firmly attached to a strong mahogany frame-work, which is itself firmly secured to a wall, and is unconnected with the floor. To this vertical bar is immoveably attached a horizontal shelf of iron, on which one of the extremities of a standard toise, placed vertically, rests. The toise is kept in its vertical position, parallel to the bar, by slight springs; and its weight is relieved, and the toise itself all but suspended, by rather less than equipoises attached to its middle; hence it is preserved of the same length in its vertical position as when laid horizontally. The upper extremity
of the bar thus placed forms the plane on which the suspension of the longer pendulum rests; and the bar being removed, the shelf on which its lower extremity previously rested, forms the corresponding plane for the suspension of the shorter pendulum. The experimental pendulums are a sphere of brass, suspended by a metallic thread. The same sphere of brass is used for both pendulums; and its height, or rather its distance below the horizontal shelf, is the same in both cases-subject only to the variations from a zero or fixed point, caused by the accidental circumstances of temperature, &c. occurring in different experiments; the value of which is determined by a microscrew. The suspension apparatus is also the same for the two pendulums; and thus the difference in the length of the metallic threads in the two cases corresponds exactly to the length of the toise at the temperature at which the experiment is made.
To the lower end of the vertical bar, below the level at which the sphere of brass is suspended, and immediately beneath the sphere, a hollow cylinder of bell-metal is fixed, in which a cylinder of steel, of seven lines diameter, works in a vertical direction, and is capable of being turned on its axis. Being made with great skill, it requires no oil, and maintains always a true vertical direction. It is raised or depressed by a micrometer screw beneath it. The value of one revolution of the screw is 0.0902 of a line, determined, experimentally, by measuring different lengths of the pendulum, corresponding respectively to observed times of vibration. The screw is turned by a lever and rack-work, so that it is not necessary for that purpose to open the general case in which the whole apparatus is inclosed, which might affect the temperature within side. The upper end of the steel cylinder is not brought into immediate contact with the sphere, but supports a horizontal steel plane at the extremity of the shorter arm of a double lever, the longer arm of which magnifies the motion sixty times. The screw is turned until the contact of the steel plane and sphere brings the longer arm of the lever to a particular mark, when the upward pressure of the plane against the sphere equals 32.84 grains; the value of which in diminishing the tension of the thread, and thus shortening its