108 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



The observing room is 43 feet long (north and south) and 

 38 feet wide. All of the walls are double. The outer of 

 the two is a louvre-work of galvanized iron which prevents 

 the sunlight from touching any part of the building proper. 

 The inner wall is of California redwood, and is separated 

 from the outer by a two foot air space. The ceiling is 

 also of redwood. It is about 16 feet above the floor. 

 Above the ceiling is an air space 8 feet high at the observing 

 slit and sloping to meet the east and the west walls. 



The observing slit is slightly over three feet in width. 

 The covering for the slit is in four parts which open out- 

 ward. The ends are closed by shutters, each of which is 

 in two parts opening inwards. Each end is also provided 

 with a single shutter which slides up and down. For stars 

 at zenith distances greater than 72 degrees these shutters 

 have to be lifted. When down they are very efficient wind 

 breaks. 



There is a large canopy which can be rolled over the 

 instrument to serve as an additional protection in stormy 

 weather or when the instrument is not in use. 



For a more detailed account of the instrument and room 

 see Astronomer Tucker's account of them in Volume IV 

 of the " Publications of the Lick Observatory, 1900." 



j. Meteo7'ology. — To make quite sure of the condition 

 of the atmosphere at any time during the observations, the 

 thermometers were read, on the average, three times an 

 hour (at nearly equal intervals); and the barometer was 

 observed every hour. The reading of the wet bulb ther- 

 mometer was also taken when the dry was read. The 

 relative humidity has not been introduced into the reduc- 

 tions, but it was thought desirable to have it for possible 

 future reductions. 



The barometer, Green 2839, hangs on the north wall of 

 the observing room. It reads to one two-hundredth of an 

 inch. The dry and the wet bulb thermometers (F) hang in 

 the air space between the north walls. The dry bulb ther- 

 mometer, used to indicate the external temperatures, is 

 Green 494. This thermometer has been calibrated at the 



