348 JOURNAL OF THE WASHINGTON ACADEJMY OF SCIENCES VOL. 11, NO. 14 



some regular body of this kind must be adopted to form the surface of ref- 

 erence for geodetic investigations as well as for geographical purposes; any 

 irregularities that may be found to exist are viewed as departures from this 

 regular form and can be taken into consideration, as such, whenever necessary. 



Since this spheroid is taken as the surface of reference, it becomes the 

 problem of cartography to take it into account in all mapping projects. 

 It is comparatively easy to determine projections of various kinds for the 

 sphere; hence mapping can be simplified if we determine an intermediate 

 projection of the spheroid conformally upon a sphere with radius equal to the 

 equatorial radius of the earth. This is done by applying a correction to the 

 geodetic latitude and results in what is called the isometric latitude. In 

 considering equal-area mapping of the spheroid with this fact in mind, the 

 idea arose that the spheroid could be projected equivalently upon a sphere of 

 equal surface by computing a correction to the geodetic latitude, the longitude 

 being left unchanged just as in the case of the conformal mapping. This 

 sphere could then be mapped upon the plane by any desired equal-area 

 projection, and the result would be an equal-area projection of the spheroid. 

 This idea of an intermediate projection was then developed analytically 

 and the resulting latitude has been christened Authalic latitude. The term 

 "authalique" was used by Tissot as a general term for equal-area. Authalic 

 latitude is therefore "equal-area" latitude. 



The difference between the geodetic latitude has been developed in a 

 Fourier series and tables computed for every half degree of latitude. These 

 results are published in U. S. Coast and Geodetic Survey Special Publication 

 No. 67, entitled Latitude developments connected with geodesy and cartography. 



The paper was discussed by Messrs. C. A. Briggs, Pawling, Sosman 

 and William Bowie. 



E. A. EcKHARDT and J. C. Karcher: A chronographic recorder of radio 

 time signals. (Presented by Mr. Eckhardt, and illustrated with slides and a 

 demonstration of the apparatus.) 



The radio time signal recorder described in this paper was devised at the 

 Bureau of Standards for the field use of the Coast and Geodetic Survey. 

 By its use the Survey will be enabled to record simultaneously on a chrono- 

 graphic drum the time signals sent out by Annapolis on the breaks of the 

 local chronometer without mutual interference. Radio signals originating at 

 Lyons, France, maybe recorded at the Bureau of Standards whenever that 

 station is sending, the air line distance between sending and receiving stations 

 being approximately 3800 miles. It is inferred, therefore, that the sensi- 

 tivity of the apparatus is sufficient to record Annapolis time signals at any 

 field station which the Coast and Geodetic Survey may occupy anywhere 

 within the borders of the United States. 



The apparatus is sufficiently rugged for field service, and a 50-foot, 6-wire 

 flat-top antenna 40 feet above the ground is sufficient for all ordinary con- 

 ditions. 



The radio apparatus proper may be used with any kind of chronograph 

 drum or tape recorder. Dot and dash signals are indicated by short and 

 long excursions of the recording pen from the datum line. In an Annapolis 

 time signal these excursions are Vs of a second long, while the pen traces the 

 datum line during 2/3 of every second. 



The receiver equipment includes a regenerative electron tube circuit in the 

 plate circuit of which there is a telegraph relay. This regenerative circuit 

 starts to oscillate when the grid potential is made to exceed a certain critical 



