IV. 
New Observations of the Planet Mercury 
By PERCIVAL LOWELL. 
Presented May 12, 1897. 
1. Observations at Flagstaff. — In the autumn of 189G I began observations on 
Mercury with the 24-inch glass of this Observatory in the hope of detecting the 
planet's period of rotation. The condition of the air by day exceeded expectation. 
The telescope had scarcely shown the planet, before attention revealed markings upon 
its surface, — markings which proved so distinct and permanent as not only to dis- 
close the planet's rotation-period, but to give in its fundamentals definite knowledge 
of the planet's self. In these observations I was assisted by Mr. D. A. Drew and 
Miss W. L. Leonard. 
2. Rotation- Period. — The rotation-period was synchronous with that of the 
orbital revolution ; thus confirming what Schiaparelli, in 1889, had discovered and 
announced, namely, th 
axis once 
of 
of the Sun. Though the results agreed with Schiaparelli's, their deter 
6" ^"^ -VK.....^ V.Q 
tion was entirely independent. 
3. Observations at Mexico. - On removing to Mexico I made another series of 
observations, during January, February, and March of this year. There, agam,^ the 
day-air proved propitious, and enabled us to confirm and extend the results obtained 
Flagstaff 
4. Method of Observation. — Before entering upon an account of them I 
give in a word or 
portant, the method by which they were secured 
since the success of the observations is due to principles which this Observatory hn 
been investiLratino-. the imDortance of which is not yet generally understood. 
First The result was not due to what most observers still consid 
of observation, a large aperture or keenness of 
This T state afte 
apertures ranging from 4 to 24 inches, and after comparison of 
of 
