Chase.] 208 ^jan. 16, 



Officer U. S. A., to the Board of Indications, to ascertain the degree of 

 accuracy. 



The following were the grounds of forecast : 



1. The mechanical influence of solar and lunar tides on atmospheric 

 currents, which has been tested by sixteen years' investigation and obser- 

 vations at Philadelphia and Haverford College. The normal tendency of 

 tidal pressure, independent of friction, polar and equatorial currents and 

 other disturbing influences, is from the East at syzygy, from the South at 

 the following octant, from the West at quadrature, and from the North at 

 the following octant, thus forming a lunar wind-rose, of a like character 

 to Dove's solar wind-rose. 



2. The normal percentage of average lunar rainfall on the several days 

 of the lunar month, as deduced from three years' observations of the 

 Signal Service Sergeants (Proc. Amer. Phil. Soc. xiv, 416-8). 



3. The Signal Service tables of the winds which are most likely, as well 

 as of those which are least likely, to be followed by rain or snow in each 

 region, during each month of the year. 



I had previously stated (Elements of Meteorology, Part i, p. 95), that 

 "a verification of lunar forecasts in five cases out of nine should be re- 

 "garded as satisfactory. In favorable localities, if due regard is paid to 

 "temporary local influences, predictions may often be made for a month 

 "in advance, which will prove true in three cases out of four." The re- 

 ports which were received from the Signal Office were examined in 

 several different ways, the lowest mean verification of lunar, influence for 

 the two days being 59 per cent., while the highest was 100 per cent., as is 

 shown by the following tests : 



I. Tests of Lunar Influence. 



a. The tri-daily bulletins of the Signal Service Bureau, show that in 

 13 of the 23 regions, or 59.1 per cent., there were such difl[erences of baro- 

 metric pressure between the two days of observation as should be pro- 

 duced by tidal influence, viz : increased pressure when the normal cur- 

 rents are retarded, diminished pressure when they are accelerated. 



/9. The normal relation of temperature to pressure (thermometer rising 

 when barometer falls, and vice versa) was shown in 17 of the 22 regions. 

 or 77 per cent. 



Y The tendency to partial reversal of surface currents by friction, in 

 passing over the land, and consequent partial opposition of lunar in- 

 fluence,* was shown in 19 of the 22 regions, or 86 per cent. 



(?. The rainfall on Christmas day was 1.07 times as great as that upon 

 New Year's day. The lunar normal ratio was 1.04:. This represents a 

 verification of 97 per cent. 



£. The influence of "favorable localities," independent of any regard 

 to " temporary local influences, " was shown in the Middle Atlantic States^ 



* Elements of Meteorol. Part i, pp. 93-5, Par. 1, 8 ; Proc. Amer. Phil. Soc, xi, 113. 



