H. H. Clayton — Seven Day Weather Period. 7 



rounded punch, are generally described as consisting of rays 

 forming with one another angles of very nearly 60°, and at 

 right angles to the rays of the above-mentioned percussion 

 figures. In the asterism of Canadian phlogopites, the rays 

 of this star-phenomenon are said to have the same direction 

 as the rays of the pressure figures. It would be interesting to 

 know whether the rays of the pressure figures do really meet at 

 angles of 60° or whether they are at right angles to the rays 

 of the percussion figures. That they cannot be both, is clear 

 from the above observations. The angle ^ probably varies 

 slightly with the temperature of the plate on which the figures 

 are made. 



Leipsic, Jan, 24th, 1896. 



Art. III. — The Seven Day Weather Period; by 

 H. Helm Clayton. 



In this Journal, vol. xlvii, March, 1 894, data were presented 

 by the writer to show the existence in the United States of six 

 and seven day periods or rhythms in the weather which appar- 

 ently resulted from, or caused, a certain regularity in the move- 

 ments of high and low pressure areas across the country. 



To enable the investigation to be extended into other 

 countries and embrace as large a part of the world as possible, 

 the trustees of the Elizabeth Thompson fund allowed a grant 

 of 200 dollars. This admitted of obtaining the assistance of 

 Mr. Arthur Sweetland in the reductions. 



Mr. A. Lawrence Rotch freely allowed the use of the large 

 amount of observational data in his possession collected from all 

 parts of the world, and by permitting the investigation to pro- 

 ceed as a part of the work of the Blue Hill Meteorological 

 Observatory he made the completed results possible. 



For the purpose of this research three stations were selected 

 in the arctic region, four in the United States, five in Europe, 

 two in Asia, two in Oceanica near the equator, three in middle 

 South America, one in Mauritius, and one in Australia. 



The work embraced the investigation of a weather period of 

 7 days 6*43 hours, another of 6 days 3*95 hours, and a third 

 of 5 days 10-8 hours. The methods and results were in each 

 case similar, and it is deemed necessary to recite in detail only 

 those obtained for the first period. Beginning with January, 

 1880, an ephemeris was constructed for the 15 years ending 



