96 REPORT OF THE SECRETARY. 



mentof "boiling" in the tul.)e are found to prevent those vexatious changes of focus 

 so common in solar work. 



These experiments, which 1 am free to say seemed to me when first proposed by 

 you of a kind to increase rather than diminish "boiling," have in fact proved 

 thus far almost wholly successful in eliminating it. The experiment with an ordi- 

 nary equatorial has not yet been tried, but for a horizontal telescope, such as is here 

 proposed, the scheme is demonstrable and feasible. 



Radiation of the (Juhan fireflij. — In continuance of your observations on the 

 cheapest forn^ of light, two specimens of Pi/ropJiorns noctilvxus were loaned to 

 the Observatory by kindness of Professor Howard, of the Agricultural Depart- 

 ment. The radiation of the thoracic-light regions of these insects was l)riefly 

 studied by the aid of the bolometer and photometer. The insect was placed 

 in the center of curvature of a concave mirror of 50 centimeters aperture and 1 

 meter focus. In the conjugate focus was the most sensitive bolometric arrange- 

 ment in the possession of the Observatory, connected to the galvanometer used for 

 holographic work. A glass plate was placed before the bolometer to cut off body 

 radiation. Nothing whatever could be observed to indicate any heating effect from 

 the light of the insect. A portion of the flame of a standard sperm candle equal in 

 area to the light spot of the insect gave such a deflection that had the radiation from 

 the insect been g-Q^xr o ^^ great in amount it could not have escaped observation. On 

 comparing the light from the candle and that from the insect by the aid of a pho- 

 tometer it was found that area for area the insect's light-giving capacity was one- 

 eighth as great as that of the candle. Its actual candlepower was igVo- ^^^ 

 counting the very considerable candle radiation not transmissible by glass, it there- 

 fore appeared that the firefly gave his light at less than xoffijo the expenditure of 

 energy required for an equal light from the standard sperm candle. You will be 

 gratified that while these observations^evidently confirm your earlier experiments 

 they show the great advance since then in the sensitiveness of the bolometer. 



PERSONNEL. 



The observing staff has l)een unchanged with the following exceptions: Dr. C. E. 

 Mendenhall was employed as temporary assistant up to August 3, 1901, and Dr. 

 N. E. Gilbert as temporary assistant, beginning June 16, 1902. 



SUMMARY. 



During the past year satisfactory progress lias l)een made in the improvement of 

 the galvanometer. Successful exjieriments have l)een made under the system first 

 proposed l)y you bj' which personal equation in transit observations is avoided, and 

 still others, which seem to be of great practical importance, by which the "boiling" 

 of the telescopic image either of sun or star shows promise of being largely overcome. 

 A comparison of the light and heat of the standard sperm candle with that of the 

 firefly showed the latter to be more than 10,000 times more economical as a source 

 of light. 



The great purpose of the observatory — the investigation of the sun and of its influ- 

 ence on the earth — has been at all times continued. 



Respectfully submitted. 



C. G. Abbot, 

 Aid Acliixj in Charge, Astrophysical Observatory. 



Mr. S. P. L.VNGLEY, 



Secretary of the Smithsonian Institution. 



