OF ARTS AND SCIENCES. 25 



Timepiece, a good watch, the errors of which were determined by 

 sextaut observations at 22^ 16"", 22^ 34 , and 1" 11™, which gave the 

 respective corrections -|-9% -\-S% -\-3\ No " black drop " was seen 

 at either internal contact. The first contact was lost; the rest were 

 observed as follows: 21'> 28'" 2% 2^ SI"" 49% 3" ll'" 50^ The 

 corrected mean times are 21'^ 28™ 10% 2^ 51™ 52% 3'' 11™ 53'; and 

 the corresponding Greenwich mean times are 2** 24™ 10% 7^ 47" 52% 

 gh ym 53s^ -pj^g sun's limb was remarkably steady at egress, but some- 

 what disturbed at ingress. 



3. Station, terrace at No. 55 Habana Street, Havana, Cuba. 

 Approximate latitude, -\-23° 9' 21" ; approximate longitude, west of 

 Greenwich, 5** 29™ 26^ Observer, Professor Charles Hasselbrink 

 (U. S. Signal Service observer in Havana). Telescope by Negretti 

 and Zambra ; apertui-e, 2.5 inches ; focal length, 39 inches; magnify- 

 ing power, 80. Chronometer Negus 582, slow 3% by comparisons 

 furnished by the observatory of Don Jose Maria Garcia de Haro, 

 semi-otficial observer for the Spanish Navy and the mercantile marine. 

 The observer recorded for himself ; the telescope was shaken by wind 

 in the afternoon. The external contacts are considered doubtful, but 

 the internal contacts were well observed. Observed times of contacts, 

 20" 33™ 57% 20'' 54™ 30% 2*^ 19™ 0% 2'^ 36™ 47^ corrected mean times, 

 20^^ 34" 0% 20'' 54™ 33% 2'' 19-" 3% 2" 36™ 50' ; resulting Greenwich 

 mean times, 2" 3™ 26% 2" 23™ 59% 7'' 48™ 29% 8" 6™ 16^ 



Just before internal contact at ingress, the observer saw a fine line 

 of light round the disk of Venus, beyond the limb of the sun. During 

 the transit, a delicate aureola of very white light was noticed around 

 the planet, suggesting the illumination of its atmosphere. Patches of 

 a dark grayish tint were noticed at times upon the deep black disk of 

 Venus. 



Photometric Observations. 



A photometer was constructed for comparing the brightness of the 

 disk of Venus during transit with that of the sky in immediate prox- 

 imity to the sun's limb. In the accompanying figure, A and B are two 

 glass prisms, the first having parallel sides, the other with sides inclined 

 at a small angle. C is a double-image prism, D a positive eyepiece, £J 

 a Nicol, and F an eyestop. A graduated circle, G, and an index, II, 

 serve to measure the angle through which the eyepiece and Nicol are 

 turned. The whole is inserted, like an eyepiece, in the tailpiece of the 

 15-iuch telescope of the Observatory. The light from the object-glass, 

 striking upon the prism A, is not deviated, but is divided by the prism 



