MORLEY AND MILLER. — THE FITZGERALD-LORENTZ EFFECT. 323 



coalesce into one. At the beginning of June the two hours are about 

 11 h. 20 m. a.m., mean solar time, and 9 h. 50 m. p.m. At the time of 

 our last set of observations, July oth to July 9th, the hours were 11 h. 

 40 m. a.m. and 8 h. 20 m. p.m., local mean time. 



After many trials, with filar micrometer, and with scale on mirror 8, 

 we found it advisable to accumulate a great number of observations made 

 as rapidly as might be. What we had to do, in presence of all the local 

 disturbances of density of the air which sometimes made observation im- 

 possible and always made it difficult, was as if we were trying to measure 

 the solar atmospheric tide. If we could vary the period of this tide at 

 will by controlling the revolutions of the earth, we should doubtless get 

 a result sooner by accelerating the latter and making a great number of 

 observations in a given time, rather than by retarding the period in order 

 to measure with very great precision the hourly height of a barometer. 

 We therefore proceeded as follows. One observer walked around with 

 the moving apparatus, his eye at the telescope, while he maintained the 

 rotation by an occasional gentle pull on a cord so fixed as not to bring 

 any strain to bear on the cross arms of the apparatus. The room was 

 darkened. The other observer also went around with the apparatus ; as 

 an index showed the azimuth of the apparatus to be that indicated by one 

 of sixteen equidistant marks, he called out the number or some other 

 signal. The first observer replied with the reading for the given azimuth, 

 which the second observer recorded. The next azimuth was called at the 

 proper instant, the reading given, and so on. Half the time, perhaps, 

 the observations were interrupted before they became numerous enough 

 to be useful, being stopped by excessive displacement of fringes owing to 

 temperature changes and the like. But patience is a possession without 

 which no one is likely to begin observations of this kind. Runs of 

 twenty and thirty turns, involving 320 or 480 readings, were not un- 

 common. A run of thirty turns meant that the observer, who could 

 sometimes make a turn of sixteen readings in sixty-five or seventy -five 

 seconds, walked half a mile while making the severe effort involved in 

 keeping his eye at the moving eyepiece without the least interruption for 

 half an hour. The work is, of course, somewhat exhausting. 



Observation with this apparatus could not begin till the month of 

 August, and we had to stop without having accomplished as much as was 

 desirable. During the busy season of the school year, observation is im- 

 possible. We had therefore expected to resume our work in June. But 

 we then found that our pine apparatus had so much suffered from the 

 dryness of the building that we could not maintain the adjustment of our 



