A Weekly Journal of Practical

WEEKLY J OURNAL OF PRACTICAL INFORMATION, ART, SCIENCE, MECHANICS, CHEMISTRY, MANUFACTURES. A AND per Annulll. Vol. XXXVIII.-No.[NEW SERIES.] 6.J NEW YORK, FJ£BRUARY 9, 1878. [$3.20[POSTAGE PREPAID.] THE HORIZONTAL PENDULUM. means of the screw, L, the instrument is made as sensitive tion of the pendulum approximate values of the masses The most minute measurements known to science are as desired by approaching to the vertical the line connecting and distances of the sun and moon' expressed in units of made by an instrument which depends for its action upon the points of attachment of the wires. The instrument is the mass and semi-diameter of the earth. He has also gravitation. It is a pendulum suspended in an exceedingly exceedingly sensitive to change of level, and the slightest pointed out that if it is found practicable to determine accu delicate manner on the principle of the torsion balance, and movement of the screw, N, is sufficient to cause the weight rately the position of the horizontal pendulum when on the the theory of its operation will be understood by the follow to move away from the reader. meridian to one minute of time, then the velocity of the pro ing simple experiment. In Fig. 3, R R represents a rigid When the weight is at rest, the suspending wires without pagation of gravitation can be measured even if it has eight rod which rotates freely on points at its ends. To the cen times the rapidity of the transmission of light through celes ter of this is attached a shorter rod carrying the weight, W. tial space, or 1 miles per second. 3. - ,480,000 If the rod, R R is horizontal, the weight will evidently hang In the large illustration, Fig. 1, is represented the modifica vertically, and if pulled aside will swing to and fro like a tion of Zollner's pendulum, invented by Professor Rood, of pendulum. Now, if the rod, R R, be raised until it becomes Columbia College, in this city, and adapted by him to the vertical, as shown iu Fig. 4, then gravity has no directing measurements of minute changes in the dimensions of solid influence upon the arm and its weight, and they remain in bodies. He has succeeded even under adverse conditions in differently pointing to any point of the compass to which measuring to the .. dlilililith of an inch, the smallest linear they may be directed. But if the rod be inclined never so magnitude which has yet been grasped within the compass little toward the horizon, gravity will act sufficiently upon of science. In order to render the column, C, rigid, Pro the weight, W, to direct the arm, A W, into a vertical plane fessor Rood attaches to it the long inclined braces, E. At J passing through the pivots of the rods, R R, and the more is shown the head of a screw, and another similar one is on inclined this rod the greater is the force required to deflect the other side of W. To these screws are fastened spiral arm and weight. springs, which confine the motion of the pendulum within The instrument based on this principle, and devised by narrow limits, and aid in leveling the same. Also to the Zollner, a noted German astronomer, in 1873, is represented torsion, the mirror, M, facing the south point of the hod pendulum is attached a wire bent in zigzags, which enters a in Fig. 2. It consists oflllt tripod with leveling screws sup" zon, and the sun or moon on the meridian, the position of box, H, filled with olive oil. This is so adjusted as to bring porting a vertical column. to which are attached two pro- the pendulum is at the point zero. When either celestial the pendulum to rest after a couple of oscillations, the oil jecting pieces, C C'. To these are fastened two delicate body is to the east of the meridian it pulls the horizontal box having an up-and-down movement by the mechanism watch springs, R R, which support the weight W. The lat· pendulum in that direction until the body reaches the meri shown. I is an index or pointer for adjusting the pendulum ter therefore constantly exerts a pull on each of the springs, dian, when no further deflectiveinfluence is shown. Then as with regard to the scale, so that the mirror may be brought R and R'. A counterpoise at P balances the weight of the body moves over to the west, the deflectiontakes place in into position to reflect the zero or center of the scale into W and its attachment. The weight carries a mirror, M, I that direction. Zollner found the instrument so sensitive to the telescope. Professor Rood suspends his pendulum by which reflects into atelescope a distant divided scale. By I these actions that he could obtain from the observed deflec- strips of copper foil. Only one of the leveling screws, ZOLLNER'S HORIZON'lAL 'PENDULUM, © 1878 SCIENTIFIC AMERICAN, INC 80 Jtituiifit �mtritau+ [FEBRUARY 9, that at L, is shown in the figure. The arm, K, is connected IS GRAVITY A MODE OF MOTION 1 with this, so that the screw can be turned through a very IN his 24th series of experimental researches Professor small angle. The levers attached to the two rear screws Faraday describes the experiments undertaken, the results are marked Rand N. One of these screws rested on the ESTABLISHED 1845. of which, he says, though" negative, do not shake my strong body whose changes in dimension were to be measured. It feeling of the existence of a relation between gravity and is evident that if one of these screws be moved up or down, MUNN & CO., Edit0rs and Proprietors. electricity, though they give nO proof that such a relation the vertical plane, passing through the points of suspension exists." In 1859, returning to the same investigations, he of the copper foil bands, would be tilted, and hence the PUBLISHED WEEKLY AT reflects upon the infinity of actions in nature, in the mutual weight and mirror would swing into a new lateral position. NO. 37 PARK ROW, NEW YORK. relations of electricity and gravity, which would come in The left hand screw attached to the arm, N, served as a mi play: he pictures the planets and comets, charging them MUNN. crometer. A scale placed under the telescope was reflected O. D. A. E. BEACH. selves as they approach the sun; cascades, rain, rising vapor, in the mirror and then read from the telescope, being thus circulating currents of the atmosphere, the fumes of a volca TERMS FOR THE SC ENT I magnified about 60 diameters. I IF C AMERICAN. no, the smoke in a chimney, become so many electrical ma . apparatus, Professor Rood One copy, one year. postage Included . ................................ $3 �O chines. Many To illustrate the delicacy of the One copy, six months, postage included .............................. 1 60 more experiments were made by Faraday, but says that "children playing on an iron bridge 360 feet dis Clubs.-One extra copy of THE SCIENTIFIC AMERICAN will be sllppliell the results were still negative, and the experimenter did not $3.20 tant caused temporary deflection of one or two divisions, gratis for every club of fivesubscribers at each; additional copies at accept them as conclusive. In this position the question same proportionate rate. Postage prepaid. and similar deviations were caused by the lower notes in an The Scientific American Supplement remains to the present day; it may be, as Professor Jevons organ in a neighboring church, the medium and higher has suggested, that the effect was too slight to be detected. mode of is a distinct paper from the SCIENTIFIC AMERICAN. THE SDPPLEMENT or it may be that the adopted notes producing no sensible effect." The general is I�sued weekly; every number contains 16 octa"o pages. with handsome arrangements were not suited experimenting is as follows: In all cases the micrometer cover. uniform in size with SCIENTIFIC AMERIOAN. Terms of subscrlpt�on to develop the particular relation which exists. screw (that moved by the lever, N) rests directly or indirectly for SUPPLEMF.NT. $5.00a year. postage paid. to subscribers Single copies The force of gravity, while conforming on one hand to 10 cents. Sold by all news dealers throughout the country. on the body the change in the dimensions of which is the Combined Rates. -The SCIENTIFIC AMERICAN and SUPPLEMENT experIenCe, is on the other a mysterious existence. We subject of study. It is first necessary to ascertain whether will be sent for one year, postage free. on receipt of seven dollars. Both know that it is proportional to mass and utterly indepen t.he different portions of the apparatus are at rest relatively papers to one address or differentaddresses, as desired. dent of present or intervening matter. In common with The safest way to remit Is by draft. postal order, or registered letter. light, sound, and to each other or approximately so. Afterward the value of Address MUNN & CO.,37 Park Row. N. Y. other influences emanating from a point, a scale division can be obtained by repeatedly moving the firSu bscriptions received and single copies of either paper sol<\oy all the law of decrease of its intensity is inversely as the the news agents. _______ arm attached to the micrometer screw by the aid of threads = = == _._._. square of the distance, yet, nnlike the former, its action leading to the observer seated at the telescope.

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