Observations of the Transit of Mercury . 193 



An examination of this kind, I consider of considerable 

 yalue, to furnish a scale or list of known phases, to which 

 to refer and compare the observed phenomena; as well as 

 to familiarize the observer with the features to be expected 

 in the actual transit, especially if he be inexperienced in 

 similar observations. 



The Helderberg party consisted of Mr. 0. S. Wilson of 

 the F. Y, State Survey, Professor G. D. Olds of the Albany 

 Academy, Mr. W. E. Johnson of the Physical Depart- 

 ment of Union College, and myself Also Mr. John 

 O'Hara and Mr. Cookingham stationed at the State Survey 

 Station " Ferris," to flash time signals. 



The instruments taken were the Clark & Son's equatori- 

 ally-mounted Comet-Seeker of the Observatory — aperture 

 3. 9 inches, focal length 42 inches, provided with position 

 micrometer, eye pieces, shades, etc. 



The DoUand Alt. — Azimuth mounted telescope of the 

 Albany Academy — aperture 2. 7 in., focal length 44 in. 



A Dent mean-solar box chronometer, a Troughton 

 10 inch Sextant, a mercurial barometer, a hypsometer 

 and wet and dry bulb hygrometer from Union College. 



A mean-solar pocket chronometer from Mr. C. Fasoldt. 



Three heliotropes, one to " Helderberg," and two to 



Ferris." A prismatic compass, an aneroid barometer, 

 a field glass, an observing tent and a fly tent from the 

 State Survey Office, also equatorial stand, lamps, blank- 

 ets, tools, etc. 



All necessary arrangements having been completed, the 

 party with its outfit left Albany on the morning of May 4th. 

 The station was reached at 6 p.m., of the same day and the 

 tents were erected and instruments placed in approximate 

 position at once. During the evening a heavy rain set in 

 which continuing for twenty-four hours, necessarily pre- 

 Tram. ix.] 25 



