536 THE POPULAR SCIENCE MONTHLY. 



number, the time of one oscillation is obtained. Of course, the 

 clock or chronometer which furnished this time might be running 

 too fast or too slow. However, it has been customary to determine 

 the rate of the timepiece by making an astronomic observation be- 

 fore swinging the pendulum and then again after. This would 

 give the amount of time gained or lost in the interim, but does not 

 prove that this amount, or even more, was not the change within 

 the interval of swinging, or that the keeping of time was not per- 

 fect while the pendulum was swung, and the error occurred either 

 before or after. 



From this uncertainty arose the need to eliminate time error, 

 and it has been most ingeniously met in the survey pendulum. 

 Here two pendulums are employed one at one station and one at 

 another, connected by a telegraph wire. Each is made to record 

 its own coincidence with a beat of one and the same chronometer, 

 so that if the chronometer has a constant rate for a minute or two 

 it is sufficient. The chronometer at the other station is then used 

 to eliminate such errors as might arise in the transmission of sig- 

 nals. In this way the relative time of the oscillations of two pen- 

 dulums is known with absolute accuracy, and from these relative 

 times relative gravity is obtained, and from relative gravity we 

 have relative distances to the earth's center, or the shape of the 

 earth. 



In this enlightened age it is not necessary to enumerate rea- 

 sons why we should know the shape of the earth. It enters as a 

 potent factor in astronomic computations ; it is indispensable in 

 map-making, and no boundary line can be drawn without its aid. 

 Besides carrying on the special cartographic functions prescribed 

 for it by law, the United States Coast and Geodetic Survey has 

 lost no opportunity to improve our knowledge of this important 

 factor, and under no regime has the survey so completely filled this 

 dual purpose as under the superintendency of Prof. Mendenhall. 



We do not measure the earth with a span, but with a pendu- 

 lum one span in length we find its shape. 



THREE hundred tombs, apparently dating from the period of the Huns, were 

 discovered last year in the commune of Cika, in Hungary. They contained bodies 

 of knights in armor, with the skeletons of their horses by their sides. The faces 

 of all were turned toward the east. The bodies were reinterred, and the articles 

 found in the graves were sent to the museum at Buda-Pesth. 



THE publication of an Index to the Names and Authorities of all Known 

 Flowering Plants and their Countries, which was contemplated by Mr. Darwin, 

 has been undertaken at the Clarendon Press, under the direction and supervision 

 of Sir J. D. Hooker. Part I of the work is now ready, and Part II is well 

 advanced. 



