Nipher — Variations in the Earth's Magnetic Field. 119 



Huron. At the former station the rainfall was 0.44 

 inch and at the latter it was 0.36 inch. At Saginaw, 

 Mich., which is south of Alpena and also on the west 

 side of Lake Huron, the rainfall was 0.26 inch. At Sault 

 Ste. Marie, at the outlet of Lake Superior, no rain fell. 

 This rainstorm was a purely local one, extending across 

 the head of Lake Michigan and along the straits of Mack- 

 inac, and probably into Lake Huron. 



On July 16, 26, 27 and 31 similar local rains occurred 

 in the same region during the midday hours. In some 

 cases there was practically no rainfall at Hessel, but the 

 clouds w^hich were observed near the horizon were recog- 

 nized as rain clouds. The weather maps show that rain 

 fell at surrounding weather stations. On all of these 

 days, the needle was in to-and-fro vibration at intervals 

 during the day. In all cases when the weather maps 

 show rains in this region, which occurred during the 

 hours of observation of the needle, the needle showed 

 such vibrations. 



On three days they were observed when violent gusts 

 of wind occurred at the station, with no rain in that part 

 of the country. 



On August 23, very marked and sudden changes in the 

 position of the needle were observed, and they were so 

 unusual as to lead to the suspicion that something un- 

 usual must have happened. There were no vibrations 

 accompanying those disturbances. The day was unusu- 

 ally clear. Very light rains occurred at all of the nearest 

 weather stations, the greatest fall, 0.20 inch, being at 

 Houghton, about 200 miles distant in a direction a little 

 north of west. 



On August 8, a violent rain accompanied by a continu- 

 ous roar of overhead thunder occurred between 4 and 

 6:30 a. m. The needle was then very quiet, as was the 

 case on every morning of the summer with one excep- 

 tion. On this morning when a few oscillations occurred 

 after sunrise, they were accompanied by violent gusts 

 of wind. 



