December 20, 1901.] 



SCIENCE, 



949 



veniently apparent. In this connection I 

 may observe that preparations have been 

 made for a south meridian mark for both 

 the 6-inch and 9-inch meridian circles, but 

 no steps have been taken during the year to 

 erect them. 



THE CLOCK SYSTEM. 



The effort to bring the department of 

 meridian observations, which is the real 

 raison d'etre of the Observatory itself, to a 

 state of the highest eflSciency and up to the 

 most modern standard of requirement, has 

 included not only a thorough overhauling 

 of both meridian instruments, but also an 

 examination, and if possible an improve- 

 ment in the clock system of the Observa- 

 tory. Critics who are in no way responsible 

 for results, and who probably would not 

 carry out their own suggestions if they were, 

 have had a standing grievance against the 

 Observatory because it has not put its 

 clocks underground. In point of fact very 

 few observatories do put their clocks 

 underground. The notable exception is 

 Pulkova. It is difficult to maintain a clock 

 underground and not ruin it by rust. The 

 experiment was tried in the very early days 

 of the Naval Observatory and abandoned 

 after the valuable Kessels clock had been 

 nearly sacrificed to the experiment. If, 

 however, a clock can be inclosed in air- 

 tight case from which the air has been par- 

 tially exhausted, it should be entirely re- 

 moved from the influences of temperature, 

 pressure and humidity, and it should, theo- 

 retically, be as safe in a vault as above 

 ground. This is the principle which has 

 governed the construction of the clock vault 

 of the Naval Observatory. The vault is 

 dug in the basement of the clock house, 

 which stands on the highest eminence in 

 the Observatory grounds, a knoll of quite 

 abrupt grades, of a gravel soil, and so situ- 

 ated that the natural drainage is away from 

 the vault in all directions. The vault is 



built with double walls and roof and thick 

 concrete floor, the space between the walls 

 being filled with nonconducting material. 

 The air of the vault is dried by gas and 

 proper provision is made for ventilation. 

 The air-tight cases containing the clocks are 

 of metal and glass, and in each is exposed 

 in full view a rust gauge of bright steel, 

 which is closely watched, and its condition 

 reported to the Superintendent at frequent 

 intervals. The Kessels clock, which is re- 

 garded as the standard, is regulated to mean 

 time, and as it is not capable of sustaining 

 the electrical connections necessary for 

 chronometric connection on the clock cir- 

 cuit, it is compared with the sidereal 

 sounder by coincidence of beats by the aid 

 of a microphone, the beats of the clock be- 

 ing wholly inaudible to the unaided ear. 

 So far the whole arrangement has proved 

 on the whole satisfactory, and the rate of 

 the Kessels clock reduced to a constant of 

 almost 0. Some trouble has been expe- 

 rienced in making the clock case actually 

 air-tight, and if the experiment (for I re- 

 gard it as no more than an experiment) 

 fails, it will be from this cause. Professor 

 Updegraff's report is herewith transmitted. 



THE 12-INCH EQUATORIAL. 



This instrument has undergone extensive 

 alterations during the year. It was re- 

 mounted in April, and has been employed 

 in charge of Assistant Astronomer Theo. 

 I. King, since that time. This instrument 

 is used for the benefit of visitors admitted 

 to the Observatory at night. 



THE PRIME VERTICAL TRANSIT INSTRUMENT 

 AND 5-INCH ALTAZIMUTH. 



These instruments have remained in 

 charge of Assistant Astronomer G A. Hill, 

 in continuation of the observations for 

 variation of latitude. 



I invite the attention of the Bureau to 

 Mr. Hill's report, as evidence of the spirit 

 in which the Observatory has been (and 



