January 21, 1892] 



NATURE 



281 



•with an aluminium frame, has been made for the Observatory 

 at Kensington, and gives every satisfaction. The comparison 

 spectrum used at Potsdam has been furnished by a Geissler tube 

 placed directly in the cone of rays of the refractor, at a distance 

 of 40 cm. from the slit, the tube being at right angles to the 

 optical axis of the refractor and the slit. The slit is set parallel 

 to the line of the diurnal motion, and widih is given to the 

 spectrum by making the driving clock move slightly slower or 

 faster than its proper rate. A uniform exposure of one hour has 

 been employed, the proper intensity bemg obtained by changing 

 the rate of the driving-clock, so that the error increases with in- 

 crease of brightness. The photographs are measured with the aid 

 of a microscope having a sliding apparatus on its table, movable 

 by a fine micrometer screw. One revolution of the screw 

 corresponds to a difference of wave-length of 0"324 y^i, which, 

 expressed in miles per second, is I39'I3. After describing the 

 methods of measuring the displacement of lines in stars of 

 different types of spectra. Prof. Vogel brings together the 

 results which have formed the subject of several previous com- 

 munications. It is said that the probable error in the deter- 

 mination of the radial velocity of a star of Class II. is ± i"34 

 miles per second, and for stars of Class I., ± 2"3I miles. 

 Measurements have been made independently by Prof. Vogel 

 and Dr. Scheiner, and each star has been observed on the 

 average 33 times, wherefore it is concluded "that the probable 

 •error of the definitive values for both spectral classes will 

 amount to less than one mile." A list of the observed veloci- 

 ties of forty-seven stars will soon be published. The mean 

 motion in the line of sight is 106 English miles per second ; 

 six stars have a velocity less than 2 miles per second, and five 

 greater than 20 miles, o Tauri heads the list with a velocity of 

 about -I- 36 miles per second. Fifteen of the stars have a 

 positive, and thirty-two a negative motion. 



Orthochromatic Plates for Astronomical Photo- 

 graphy. — MM. Fabre and Andoyer photographed the eclipsed 

 moon at Toulouse Observatory on November 13, 1891 ; and some 

 of the pictures obtained were exhibited by them at the meeting 

 of the Paris Academy of January 1 1, with a note on the 

 method of production. Collodion -bromide and collodion- 

 chloride plates were employed, both kinds being treated with 

 -eosin and cyanin to render them orthochromatic. The former 

 kind of plate was found to be relatively more sensitive to red 

 and yellow rays than the latter, although both were stained 

 with the same dyes. It is proposed, therefore, to use collodion- 

 bromide orthochromatic plates to obtain photographs of Mars, 

 Jupiter and the red spot, and coloured stars. 



DREDGING OPERA TIONS IN THE EASTERN 



PACIFIC. 

 'T'HE Bulletin of the Museum of Comparative Zoology at 

 Harvard College, published in June, contains three letters 

 from Prof. Alexander Agassiz to the Hon. Marshall McDonald, 

 United States Commissioner of Fish and Fisheries, on the 

 ■dredging operations off the west coast of Central America to 

 the Galapagos, to the west coast of Mexico, and in the Gulf of 

 California. The operations, which were in charge of Prof. 

 Agassiz, were carried on by the U.S. Fish Commission steamer 

 Albatross, Lieutenant Commander Z. L. Tanner, U.S.N., 

 commanding. 



I. 



Steamer " Albatross" Panama, U. S. of Colombia, 

 March 14, 189 1. 



My dear Colo.nel McDonald,— We returned yesterday 

 from our first trip. The route extended from Panama to Point 

 Mala, and next to Cocos Island ; from there we ran in a 

 southerly direction, then northwesterly to Malpelo Island, and 

 back to the hundred-fathom line off the Bay of Panama, We 

 spent several days trawling off the continental plateau of the 

 Bay. This trip being rather in the nature of a feeler, I cannot 

 tell you just what I think it means. But I believe I can to 

 «ome extent conjecture probabilities from what has been 

 accomplished. 



I have found, in the first place, a great many of my old West 

 Indian friends. In nearly all the groups of marine forms among 

 the Fishes, Crustacea, Worms, Mollusks, Echinoderms, and 

 Polyps, we have found familiar West Indian types or east coast 

 <brms, and have also found quite a number of forms whose wide 



geographical distribution was already known, and is now ex- 

 tended to the Eastern Pacific. This was naturally to be ex- 

 pected from the fact that the district we are exploring is 

 practically a new field, nothing having been done except what 

 the Albatross herself has accomplished along the west coast of 

 North and South America. The Challenger, as you will re- 

 member, came from Japan to the Sandwich Islands, and from 

 there south across to Juan Fernandez, leaving, as it were, a 

 huge field, of which we are attacking the middle wedge. As 

 far as we have gone, it seems very evident that, even in deep 

 water, there is on this west coast of Central America a con- 

 siderable fauna which finds its parallel in the West Indies, and 

 recalls the pre- Cretaceous times when the Caribbean Sea was 

 practically a bay of the Pacific. There are, indeed, a number 

 of genera in the deep water, and to some extent also in the 

 shallower depths, which show far greater affinity with the 

 Pacific than with the Atlantic fauna. Of course, further ex- 

 ploration may show that some of these genera are simply genera 

 of a wider geographical distribution ; but I think a sufficiently 

 large portion of the deep-sea fauna will still attest the former 

 connection of the Pacific and the Atlantic. 



I am thus far somewhat disappointed in the richness of the 

 deep sea fauna in the Panamic district. It certainly does not 

 compare with that of the West Indian or Eastern United States 

 side. I have little doubt that this comparative poverty is due to 

 the absence of a great oceanic current like the Gulf Stream, 

 bringing with it on its surface a large amount of food which 

 serves to supply the deep-sea fauna along its course. In the 

 regions we have explored up to this time, currents from the 

 north and from the south meet, and then are diverted to a 

 westerly direction, forming a sort of current doldrums, turning 

 west or east or south or north according to the direction of the 

 prevailing wind. The amount of food which these currents 

 carry is small compared with that drifting along the course of 

 the Gulf Stream. I was also greatly surprised at the poverty 

 of the surface fauna. Except on one occasion, when, during a 

 calm, we passed through a large field of floating surface mate- 

 rial, we usually encountered very little. It is composed mainly of 

 Salpae, Doliolum, Sagittas, and a few Siphonophores — a striking 

 contrast to the wealth of the surface fauna to be met with in a 

 calm day in the Gulf of Mexico, near the Tortugas, or in the 

 main current of the Gulf Stream as it sweeps by the Florida 

 Reef or the Cuban coast near Havana. We also found great 

 difficulty in trawling, owing to the considerable irregularities of 

 the bottom. When trawling from north to south, we seemed 

 to cut across submarine ridges, and it was only while trawling 

 from east to west that we generally maintained a fairly uniform 

 depth. During the first cruise we made nearly fifty hauls of the 

 trawl, and, in addition, several stations were occupied in trawl- 

 ing at intermediate depths. In my dredgings in the Gulf of 

 Mexico, off the West Indies, and in the Caribbean, my atten- 

 tion had already been called to the immense amount of vegetable 

 matter dredged up from a depth of over 1500 fathoms, on the 

 lee side of the West Indian Islands. But in none of the dredg- 

 ings we made on the Atlantic side of the Isthmus did we come 

 upon -such masses of decomposed vegetable matter as we found 

 on this expedition. There was hardly a haul taken which did 

 not supply a large quantity of water-logged wood, and more or 

 less fresh twigs, leaves, seeds, and fruits, in all possible stages 

 of decomposition. This was especially noteworthy in the line 

 from the mainland to Cocos Island, and certainly offers a very 

 practical object-lesson regarding the manner in which that island 

 must have received its vegetable products. It is only about 275 

 miles from the mainland, and its llora, so similar to that of the 

 adjacent coast, tells its own story. Malpelo, on the contrary, 

 which is an inaccessible rock with vertical sides, and destitute 

 of any soil formed from the disintegration of the rocks, has re- 

 mained comparatively barren, in spite of its closer proximity to 

 the mainland. 



The most interesting things we have found up to this time are 

 representatives of the Ceratias group of Fishes, which the 

 naturalists of the Albatross tell me they have not met before on 

 the west coast of North America. The Crustacea have supplied 

 us with a most remarkable type of the Willemoesia group. The 

 paucity of Mollusks, and also of Echini, is most striking, 

 although we brought up in one of the hauls numerous fragments 

 of what must have been a gigantic species of Cystechinus, 

 which I hope I may reconstruct. We were also fortunate 

 enough to find a single specimen of Calamocrinus off Morro 

 Puercos, in 700 fathoms, a part of the stem with the base. 



NO. II 60, VOL. 45] 



