948 



SCIENCE. 



[N. S. Vol. XIV. No. 364; 



Anderson, who had been assistant on this 

 instrument for twenty-six years, which oc- 

 curred in November last, and to the ab- 

 sence after February 1 of the party sent out 

 by the observatory to observe the eclipse of 

 the sun in Sumatra, Professor See worked 

 entirely alone for a part of the year. 

 The manual labor alone in using this in- 

 strument is considerable, and I consider 

 the showing made in Professor See's report 

 as creditable. This instrument has been 

 devoted to the same general line of work as 

 in previous years, and has been maintained 

 in good order. Professor See's report is 

 herewith transmitted. 



THE 9-IlsrCH TRANSIT CIRCLE. 



This instrument has been steadily em- 

 ployed on the regular sun, moon, and planet 

 work, a revision of the Astronomische Ge- 

 sellschaft Zones, and the Zone of Zodiacal 

 Stars undertaken for the Paris Astronomi- 

 cal Conference of 1896. From long service 

 this instrument is in need of important re- 

 pairs. The pivots have become so worn as 

 to need regrinding, and the illumination 

 should be changed so that the reticule will 

 be illuminated by a beam of light in the 

 optical axis of the instrument, instead of a 

 beam cast from one side, as at present. As 

 soon as the alterations of the 6-inch transit 

 circle, which are noted later, are completed, 

 the whole staff for meridian observations 

 will be transferred to that instrument, and 

 the 9-inch transit circle will be put under 

 repairs. The report of Assistant Astrono- 

 mer King, in charge of the instrument at 

 the close of the fiscal year, is transmitted 

 herewith. 



THE 6-INCH TRANSIT CIRCLE. 



Since this instrument was mounted two 

 years ago a serious defect in the form of a 

 diurnal change in the constant of azimuth, 

 following changes of temperature, has been 

 a source of annoyance and embarrassment 

 and a serious detriment to the usefulness 



of the instrument. Since March last a sys- 

 tematic and patient investigation of this 

 defect has been carried on by Professor Up- 

 degraff with the object of "determining, 

 and if possible, removing the cause. Suc- 

 cessive changes have been made in the in- 

 strument and its supports as a result of this 

 investigation, without in any way altering its 

 form (which could not be done without en- 

 tirely rebuilding it) , and there is reason to 

 believe that the success of these changes is 

 already assured. 



This instrument was built by Messrs. 

 Warner & Swasey, of Cleveland, Ohio, 

 from designs by Professor William Hark- 

 ness, U. S. N., following closely the pattern 

 of the latest instruments by E-epsold, of 

 Hamburg. It would be presumptuous to 

 criticise the result of the experience of 

 the oldest and most skilful instrument- 

 makers in the world, and yet I can 

 not believe that this form of instrument 

 will ever be entirely free from uncertainty 

 in the errors of azimuth or level, or both, 

 for the reason that in order to assure pre- 

 cision in other respects a principle has been 

 sacrificed which has been recognized as 

 fundamental in the construction of astro- 

 nomical instruments for at least two hun- 

 dred years, viz. , that the instrument itself 

 should be directly supported on a substan- 

 tial foundation of masonry. In this form 

 of instrument the pivots are supported by 

 a skeleton work of metal by which they are 

 raised sixteen inches above the piers. Dif- 

 ferences in the rate of expansion between 

 the masonry of the piers and the metal sup- 

 port of the pivots become immediately ap- 

 parent in the azimuth or level of the in- 

 strument, and some evidence of this will, I 

 believe, be always apparent. If these errors 

 can be reduced to something manageable 

 under normal conditions, there will still re- 

 main the probability that abnormal condi- 

 tions and sudden and excessive changes of 

 temperature may still make them incon- 



