TO 



NA TURE 



[May I, 1890 



to these rotating plates made the whole automatic, the 

 driving power being compressed air under electric control. 

 A form of sand-clock was found most efficient for counter- 

 acting the diurnal motion. 



For the total phase our preparations were even more 

 elaborate. What I attempted was nothing short of the 

 complete automatic operation of all the photographic 

 instruments, whether photometers, spectroscopes, cameras, 

 or polariscopes. Over a score of these instruments were 

 securely adjusted upon an immense polar axis, split, and 

 mounted on the English plan. Powerful clock-work with 

 a Repsold governor carried the whole with great accuracy. 

 All such mechanical movements were specially invented 

 and constructed as were necessary to work the exposing- 

 shutters, to change exposed plates for fresh ones, and to 

 perform all other operations, as rotating Nicols, varying 

 apertures of objectives, trailing plates, and the like. Each 

 movement, of whatever sort, took place as a result of the 

 thrust of a small, collapsible, pneumatic bellows. The 

 precise instants of collapse of these bellows were controlled 

 through the intervention of the Gaily pneumatic valve, a 

 most ingenious device whereby any required number of 

 very small air-currents (exhaust) are made to control the 

 motion of an equal number of large air-currents (also 

 exhaust). This principle has been very successfully em- 

 ployed in the automatic playing of musical instruments ; 

 and anyone familiar with the modern forms of these, in 

 which a perforated paper sheet takes the place of the 

 music, will readily comprehend how the whole thing was 

 done. In the pneumatic commutator actually used at the 

 African station forty- eight half-inch currents were under 

 absolute control of a small paper sheet, about nine inches 

 wide, suitably perforated, and unwinding at an invariable 

 rate from a chronograph barrel. Thence it passed over 

 the series of minute apertures through which flowed 

 the lesser exhaust-currents, each of which controlled the 

 action of its own valve, and consequently of its appropriate 

 large exhaust-current, through suitable pipes leading to 

 the individual pneumatic bellows. A portion of the 

 <;ommutator-sheet is represented in the illustration. 



I do not need to specify here the detail of astronomical 

 apparatus which this pneumatic commutator operated ; but 

 in the collection of totality-instruments were two 8-inch 

 silver-on-glass mirrors, four spectroscopes, and a variety 

 of objectives for a variety of purposes, ranging all the way 

 from a |-inch aperture in one of the polariscopes to the 

 Harvard 8-inch doublet of 13 feet focal length. The 

 whole number of plates, or separate exposures, was in 

 ■excess of 300, totality being 190 seconds in duration ; 

 and- when once started, the whole affair looked out for 

 itself absolutely, so long as the necessary power was 

 supplied at the main exhaust-bellows. 



But totality was completely clouded under ; and instead 

 of a fine accumulation of photographic data, I have only 

 the gratification of having shown it to be practicable in 

 the future for one eclipse observer to operate an indefinite 

 amount of photographic apparatus quite as readily as, 

 and with greater certainty than, he would have attended 

 to only two or three cameras by hand heretofore. In con- 

 verging all this apparatus toward readiness for eclipse- 

 day, I had of course much valued assistance, which will 

 be fully acknowledged elsewhere ; and I need only 

 mention here Prof Bigelow, Mr. Davis, and Mr. Van 

 Guysling, who were specially helpful in devising required 

 movements and practically constructing them. 



The totality-area in West Africa appears to have been 

 unusually overcast. Auxiliary observers at Cabiri had 

 clouds ; at Cunga, clouds ; at Dondo, clouds ; while at 

 Cazengo, Oeiras, Muxima, Kakulu, and Bom-Jesus it was 

 cloudy too. Also, about 15 miles out at sea, in the path 

 of central eclipse, whither the Pensacola had gone in the 

 hope of additional results, the sky-conditions were per- 

 haps slightly better, but still so bad that it is doubtful 

 whether the true corona was seen at all. 



Lest I weary anyone who may be reading this with too 

 long a statement of our work, I omit here all account of 

 the natural history of the Expedition, only saying for 

 the present that Messrs. Brown, sent out by the U..S. 

 ^National Museum, have been actively engaged in collect- 

 ing at all the ports made by the Pensacola, and their 

 materials will, I dare say, be competently discussed on 

 the return of the Expedition. More about this later. 

 At Ascension, opportunity for trawling is now for the 

 first time available, and so far with fair success. While 

 the main eclipse party was established at Cape Ledo, 

 naturalists and anthropologists were in the interior about 

 three weeks, at Cunga and at Uondo, His Excellency the 

 Governor of Loanda, and the Directors of the Caminho 

 de Ferro Trans-Africano, having courteously afforded 

 them every facility for the prosecution of their work 

 there. Physical measurements were taken among the 

 Umbundus, Cabindas, Bailundas, Ouissamas, and others ; 

 collections of folk-lore, fetishes, and mind-products made ; 

 and general information gathered concerning a variety of 

 subjects indicated in the manual of the Anthropological 

 Society of Great Britain. On reaching the Cape, both 

 naturaHst and anthropologist found the outlook so pro- 

 mising that they applied for discharge from the Expe- 

 dition there, in order to continue their work in the Cape 

 peninsula. The opportunities were indeed rare : a great 

 exploring Expedition was about organizing, under the 

 auspices of the English Syndicate, to which the King of 

 the Matabele has granted unusual privileges and conces- 

 sions, in a region for the most part untravelled by white 

 men, and represented as very rich in material for natural 

 history and other research. The Expedition is particu- 

 larly indebted to the Rev. G. H. R. Fisk, of Cape Town, 

 for a very valuable collection of tortoises, embracing 

 Testudo pardalis, T. angiilata, T. irtmeni, and T. ten- 

 ioria; Hotnopiis areolatus, H.femoralis, and H. signatus, 

 the representatives of these latter forming a perfect series 

 of the South African Homopus. 



The progress of M. Heli Chatelain's researches in the 

 West African tongues is gratifying, and bids fair to con- 

 stitute a valuable section of the work of the Expedition. 

 He remains in Angola for some months yet, to gather 

 linguistic material for various works he has in hand — 

 among them his " Grundziige des Ki-mbundu," in which 

 the elements of this language are compared with those of 

 Kixi-kongo, Luba, Lunda, N-mbundu, Oshi-ndonga, and 

 Otyi-herero. The results will enable one to form an 

 idea of the mutual relations of the languages of Central 

 West Africa. 



I may say here that Prof. Bigelow, in addition to assist- 

 ing in the pendulum-work at St. Helena and Ascension, 

 has been diligently engaged upon theoretic researches on 

 the corona and terrestrial magnetism, the beginnings of 

 which are outlined in his paper already published by the 

 Smithsonian Institution. As yet he inclines to speak of 

 this work with much reserve ; but if the key to the solu- 

 tion of these complex phenomena has not actually been 

 found, it surely looks strongly that way. By Dr. Gill's 

 kindness, the resources of the excellent library of the 

 Cape Observatory were freely and gladly drawn upon in 

 this work. . . ., -. 



Of the Bulletins, or preliminary publications of the 

 Expedition, thirteen are already issued — one each relating 

 to general matters, to terrestrial physics, to philology, and 

 to localities of scientific interest in St. Helena; two to 

 meteorology and to natural history ; and five to the total 

 eclipse. 



I reserve for another occasion all account of the im- 

 portant researches which Prof Cleveland Abbe, Meteoro- 

 logist of the Expedition, has been sedulously prosecuting 

 for the past five months and over, with improved means, 

 and under rare conditions at sea and on land. 



David P. Todd. 



U.S.S. Pensacola, Ascension, March 27. 



