674 REPORT — 1900, 



large exhaust iDellows by lead tubes of small calibre. The operation of the pockets 

 ■was controlled through a pneumatic commutator, the control sheet being of paper, 

 and having perforations at such points as corresponded to the mechanism or 

 instrument desired. This sheet unwound from the barrel of an ordinary chrono- 

 graph, -which thereby not only regulated the exposures, but recorded their exact 

 times. Twenty-two photographic instruments were controlled by this scheme of 

 operation at Cape Ledo, West Africa, on December 22, 1889. 



(h) The electric system devised and built for the Amherst Eclipse Expedition 

 to Japan, 1896, through the liberality of ISIessrs. Willis and Arthur James, of 

 New York, who sent the expedition out in their yacht Coronet} The power 

 requisite for the automatic movements was here derived for the most part from 

 spiral springs, the recoil of which was governed by specially devised escapements 

 operated by ordinary electro-magnets. The control currents were sent through a 

 commutator - which was originally a chronograph, the cylinder being replaced by 

 a copper barrel, in which pins were inserted at suitable points for making contacts 

 with the teeth of a copper comb. Thus, as in the pneumatic system, the commu- 

 tator regulated the exposures and recorded their times as Avell. Twenty photo- 

 graphic instruments were controlled by this scheme of operation at Esashi, Japan, 

 on August 9, 180G. 



(e) The mechanical system, devised and built for the expedition to Tripoli, 

 1900, and at the charges of Mr. Percival Lowell, of Boston. By the courtesy of 

 the Hon. T. S. Jago, H.B.M.'s Oonsul-General at Tripoli, the station was 

 established on the terrace or roof of the British Consulate. This location aflbrded, 

 among other advantages, an exceptional chance of utilising gravity as a motive 

 power for the mechanical operation of shutters and plate-holders by means of 

 cords wound upon pulleys which turned the axles, the cords being pulled by small 

 weio-hts which descended within the interior court of the Consulate. This system 

 not having been invented until after my arrival in Tripoli, its construction was neces- 

 sarily crude and provisional. In addition to the help of native artisans I had 

 the very efficient assistance of Messrs. W. H. Venables and W. F. Riley, of the 

 English colony in Tripoli. The commutator was again a barrel, improvised from a 

 large oil-drum", and turned by a cord and heavy weight, its speed being regulated 

 to the requisite accuracy by a fan governor. By the courtesy of Mr. James A. 

 Doughan this was built in the machine shops of Messrs. Perry, Bury, & Company. 

 From the commutator barrel there unwound also seven cords which passed over 

 pulleys to the various mechanical movements of the .shutters and plate-barrels, 

 held in position by escapements similar to those used in Japan for the previous 

 eclipse ; and upon these cords were fastened large beads at intervals suited to the 

 exposures required. Each bead in pas.«ing the escapement tripped it, thus 

 allowing gravity to advance the movement by a single stage or unit. Seven 

 instruments were operated on this system during the recent eclipse at Tripoli, and 

 about one hundred photographs secured. 



Experience with these three systems leads me to the conclusion that with 

 slio-ht modifications the last is simplest and best for the automatic operation of a 

 Tery few instruments. But a combination of the first and second is best for a large 

 number of instruments, the mechanisms being no more likely to get out of order 

 than the similar movements in the pneumatic and electric action of a modern 

 church organ, and no more likely to tail of the right exposure on the right plate 

 at the right time than such an organ is likely to sound a false or unintended note. 



3. On the Adaptation of tlie Principle of the Wedge Photometer to the 

 Bior/raph Catnera in photo [jraphing Total Eclipses. Bij Professor 

 David P. Todd, M.A., Ph.D., Director of the Observatory of Amherst 

 College', U.S.A. 



This paper describes an instrument devised for photographing the recent eclipse 

 —both the slender partial phases and the coroni on a single film, with correctly 



llie Astrophysical Journal, vol. v., p. 318. 

 •* Stari and Telescopes, by Professor David P. Todd (Sampson Low, Marstb'n, & 

 Co., 1900), p. 363. 



