423 



THE POPULAR SCIENCE MONTHLY. 



serted in it, and a conical steel needle-drill 

 is introduced into the central hole of the 

 metallic cylinder thus formed. The piston- 

 head of the perforator is then made to strike 

 upon the head of the needle, so as to drive 



it in like a wedge and cause it to force the 

 two segments apart and split the rock. As 

 many holes may be made as are necessary 

 to break the rock up, and this depends much 

 upon its hardness. Fig. 5 represents a sec- 



Fig. 5. Section of a Gallery under a Coal-Mine, indicating the Holes to be bored by 

 the Perforator, so as to break up the Sterile Rock in Four Successive Operations. 



tion of the chamber of a coal-mine, and in- 

 dicates the position of the holes that have 

 to be drilled to break up the rock in four 

 successive operations. The inventors of this 

 apparatus claim that rock can be broken up 

 with it in veins of the average thickness 

 almost as fast as with gunpowder. 



Transmission of VibrationSo The Trans- 

 actions of the Seismological Society of Ja- 

 pan contains an account of experiments by 

 Professor H. M. Paul, in Washington, D. C, 

 on the transmission of vibrations from rail- 

 road-trains through the ground. Cups con- 

 taining mercury were fixed at four stations, 

 at distances of from 0*29 to 0*93 of a mile 

 from the railroad, in which the amount of 

 disturbance caused by vibration was ascer- 

 tained by noticing the displacements of the 

 reflected image of the pole-star. The char- 

 acter of the effects varied according to the 

 distance of the station from the train, the 

 nature of the ground at the station, and the 



j kind of train, but they were distinct. At 

 I one of the stations the communication of 

 vibrations, which were limited to a shallow 

 depth, appeared to be interrupted by the 

 intervention of a ravine. The effect of car- 

 riage-driving on a public road was also ob- 

 served. A hack carrying four persons and 

 drawn by two horses, about four hundred 

 feet away, caused a temporary shaking of 

 the mercury whenever a wheel struck a stone 

 or hollow; and a similar effect was pro- 

 duced while the carriage was crossing a 

 small wooden bridge at about five hundred 

 feet ; but no serious continuous disturbance 

 was perceived till the carriage approached 

 within two or three hundred feet of the in- 

 strument. 



The Systematic Position of the Braclii- 

 opoda. In the " Jcnaische Zeitschrif t f iir 

 Naturwissenschaft," Jena, 1881, Dr. Oscar 

 Uertwig and Dr. Richard Hertwig, the emi- 

 nent embryologists, recognize the work of 



