A. MATHEMATICS AND ASTRONOMY. 3 



described as the locus of the feet of a, series of perpendiculars 

 let foil upon all possible tangents to a circle, from a point 

 outside the circle, and at a distance from the centre thereof 

 equal to its diameter. The conchoid is likewise easily de- 

 scribed graphically by a point fastened to a given circle 

 which rolls around a fixed circle, provided that the two cir- 

 cles have the same diameter, and that the point be fastened 

 to the rolling circle at a distance from its centre equal to the 

 diameter thereof. Miith. der JSFaturf. Gesett., Berne, 1873, 31. 



STANDARD TIME IN PITTSBURGH. 



The question of the regular distribution throughout the 

 community of standard uniform time has been well tested by 

 Professor Langley, of Pittsburgh, who, during the past five 

 years, has steadily extended the system of telegraphic con- 

 nections between the astronomical observatory of that city 

 and the railroads that centre therein. The magnificent new 

 City Hall has in its turret a large tower clock, built by the 

 Messrs. Howard of Boston, which by electrical connections 

 is made to beat, second by second, in perfect unison with the 

 standard clock at the observatory. A person at the latter 

 building can, if necessary, even adjust the tower clock by 

 telegraph, and can at any moment ascertain whether its in- 

 dications are correct or not. The large bell of the tower is 

 struck with the utmost accuracy at noon, and at every third 

 hour throughout the day and night, and the public apprecia- 

 tion of the convenience and utility of the general system of 

 absolutely accurate time is noticed in the universal compari- 

 son of watches daily at the stroke of noon. This ordinarily 

 causes a movement so general and simultaneous throughout 

 the city as on the one hand to amuse a stranger, and on the 

 other hand to demonstrate how nervously anxious Americans 

 are to secure the highest attainable accuracy in the time- 

 keepers on which they depend for the regulation of private 

 as well as public business. During nearly two years that 

 the system has been in operation it is stated that there has 

 not been any interruption from the failure of electric mecha- 

 nism, and the utility of the system certainly more than justi- 

 fies the expense which the city has been to in establishing 

 this now recognized public necessity, which can not hereafter 

 be dispensed with. In fact, the amount of time wasted 



