302 



SCIENCE. 



[Vol. I., No. 11. 



minutes later. No phenomena worthj^ of note 

 were seen between third and fourth contacts. 

 The lapping of the limb of Venus over that 

 of the sun gradually but steadily decreased, 

 until the final separation was observed with 

 great accuracy for such a phenomenon. Soon 

 after the last contact, the entire apparatus was 

 again carefull_y examined, and the necessary 

 observations made to determine the errors of 

 the chronometers. All the measures were 

 made, also, for determining the exact position 

 of the photoheliograph. 



The dry plates were developed in a few days ; 

 and 146 dry plates and 30 wet ones were sent 

 to Washington, all of which can be easily 

 measured. Two dry plates were exposed in 

 the forenoon, when the clouds were too dense, 

 and no images were obtained ; and two others 

 were accidentalh- broken. 



In the observations of interior contacts there 

 was no trace of any tremor or fluctuation of 

 the light in the cusps, as they closed around 

 the limb of Venus ; and it is almost needless 

 to say, that there was no trace of a shadow or 

 a black drop or ligament between the limbs at 

 second and third contacts. The probable 

 error of the second and third contacts was es- 

 timated at 0.3s. ; for fourth contact, 0.5s. 



Observers of transits of Venus and Mercury 

 have written so much in regard to the obstacles 

 encountered from the apparition of the shadow 

 or black drop between the limbs of the two 

 bodies at second and tJih'd contacts, and so 

 full has been the testimony in favor of the ex- 

 istence, and the almost necessarj- occurrence, 

 of this phenomena, that, at the transit of Mer- 

 cury in 1878, manj' observers claimed, as evi- 

 dence of their skill, that they did see it, while 

 others less fortunate apologized for not seeing 

 it. Observers of the black drop were so gen- 

 erallj' confined to those with imperfect appa- 

 ratus, or to those unaccustomed to observations 

 of the sun's limb or disk, that the true nature 

 of the obstacle was prettj' well understood 

 before it was carefully' investigated. It is now 

 quite well settled, that the ' black drop ' is due 

 to bad eyes, imperfect apparatus, or the inex- 

 perience of the observer. With good ej'es and 

 proper apparatus, a good observer never should 

 see the black drop : for, when it is seen, there 

 is something wrong ; it is a spurious phe- 

 nomenon. 



not seem to be generally appreciated, and I 

 Ijnow of onlj' one contrivance adapted to it 

 other than the one to be described. This one 

 can be called a time-transmitter from its re- 

 semblance in appearance and action to the 

 Blake transmitter in ordinary telephones. It 

 is the .invention of Mr. C. W. Ruehle of De- 

 troit, and has been in use at the observatory at 

 Ann Ai-bor for about six months. Its beha- 

 vior is in everj'' way satisfactory. 



Its general character can be seen from the 

 accompanying figures. Fig. 1 is the face view 

 of the transmitter. At a, a are the binding- 



A TELEPHONIC TIME-TRANSMITTER. 



Among the various methods of distributing 

 time, the telephone affords one commendable 

 for its simplicity. Its use for this purpose does 



posts for the wires from the battery ; 6, &, those 

 for the wires of the telephonic circuit. Between 

 the latter is a switch, not represented in the 

 drawing, which enables the operator to cut out 

 the telephone circuit when any thing goes 

 wrong, c is a button, by pressing which the 

 instrument can be set going. When started, it 

 runs for two and one-half minutes, during which 

 time the hand in the centre completes a revolu- 

 tion. At the end of that time it stops, and can 

 be started again only by pressing the button. 



In Fig. 2 we have a view of the interior. 

 We have here ordinary clock-work, with the 

 addition of a Ruhmkorfi" coil at d, the unlock- 

 ing part e, a circuit-breaker at/, and an inter- 

 mitting-wheel g. This wheel moves to the right. 



