REPORT OF THE SECRETARY. 73 



city, subject to all sorts of ground and electric tremors, when the elimination of 

 these tremors is so vitally necessary to success. While the effects, due to A'ibration, 

 have been greatly reduced by means already alluded to, yet they still exist. It may 

 be incidentally observed that experiment has shown that these small ground tremors 

 are only about one-third as great at night as in the day, a condition owing to the 

 difference in the amount of traffic in the neighboring streets. Experiments were 

 also to be made to compare the magnetic disturbances due to electrical causes with 

 those at the magnetic station at the United States Naval Observatory without the 

 city, but only a small difference in favor of the latter site was found. Induction 

 effects in the bolometer circuit might have been expected to be caused by electric 

 currents in neighboring street lines; but owing to the special winding of the coils 

 and careful arrangement of all connections this disturbance has been much smaller 

 than has been anticipated. When all is said, however, it unfortunately remains 

 true that the best results can never be reached in the present situation. 



C. Accessions of Apparatus. 



The principal accessions of apparatus during the past year are as follows: 



1. A 6-inch telescope with photographic and visual objectives, 4 eyepieces, 2 ampli- 

 fying lenses, and spectroscopic attachment. 



2. Special camera for exposing the moving plate in making holographs. 



3. A slit with 12-centimeter jaws for use in place of cylindric lens in producing 

 linear translations of holographs. 



4. Special rheostat with slide wire all inclosed by water jacket for use in the 

 bolometer circuit. 



5. Great battery of 60 storage cells for the bolometer circuit, with appropriate 

 switch for charging and discharging. 



6. Temperature controlling apparatus. 



7. A new governor for the siderostat. 



8. Stereoscopic camera. 



9. Telephoto camera. 



10. Projection lantern with accessories. 



PERSONNEL. 



Mr. C. G. Abbot succeeded Mr. R. C. Child as aid acting in charge, January 1, 

 1896. Mr. R. C. Child left the observatory June 30, 1896. Mr. L. E. Emerson was 

 appointed as assistant on June 26, 1896. 



I may sum up the results of the last year's work in saying that an entirely new stage 

 of accuracy has been reached by the elimination of sources of error of long stand- 

 ing, and that as a result of this accuracy between 200 and 300 well-determined lines 

 may be expected to appear in a communication which it is expected in the next year 

 to publish. 



Respectfully submitted. 



C. G. Abbot, 

 - Aid Acting in Charge, Astrophysical Observatory. 

 Mr. S. P. Langley, 



Secretary of the Smithsonian Institution. 



