Yucatan at the same depths, and that this fauna extends over the greater part of the Gulf of Mexico. The mud about the mouth of the Mississippi produces a decided change in the fauna; in the deep water off the mouth of the river nothing of importance was obtained by the dredge, but in depths of 118 to 500 fathoms a number of interesting specimens were secured.

The following extract from a letter of Capt. Sigsbee, commanding the S. S. Blake, is of considerable interest:

On the first of April we put to sea again [from Havana]; we steamed about one and a half miles from the Morro (East), and at the third haul in 177 fathoms, from disintegrated coral rock bottom, up came six beautiful "sea lilies." Some of them came up on the tangles, some on the dredge. They were as brittle as glass. The heads soon curled over and showed a decided disposition to drop off. At a haul made soon after we got more, and being afraid to put so many of them in the tank together, I tried to delude the animals into the idea that they were in their native temperatures by putting them into ice-water. This worked well, although some of them became exasperated and shed some of their arms. They lived in the ice-water for two hours, until I transferred them to the tank. They moved their arms one at a time. Some of the lilies were white, some purple, some yellow; the latter was the color of the smaller and more delicate ones. All the sea lilies were obtained from the same place."

Some twenty perfect specimens of these beautiful Pentacrini were obtained, representing the two recognized species, but Prof. Agassiz is inclined to consider P. Mülleri as a younger stage of P. Asterias.

The work on the Blake has been of great value in determining the hydrography of the Gulf, as is well shown by a small map prepared at the Coast Survey office. This map is made up from the British Admiralty and U. S. surveys.

"The map speaks for itself, and I need only call attention in a general way to the principal features of the bottom. The most striking characteristics of the Gulf are the two great banks extending the one to the west of Florida peninsula and northward of the Florida Reef, the other northward of the peninsula of Yucatan, the 100-fathom line in both cases running in a general way parallel to the shore line and forming the edge of the steep slopes of the deeper parts of the central portion of the Gulf of Mexico. The rapidity with which the depth increases is very strikingly shown to the north of the Tortugas, and to the northward and westward of Alacran Reef, by the proximity of the 100 and 1,800 fathom curves, the eastern and southern edges of the

central basin of the Gulf of Mexico having thus very steep sides, while the western and northern slopes are far more gradual. The north slope off Cuba is also quite abrupt, while the southern slope of the Florida Reef into the trough of the Gulf Stream is comparatively gentle."

This letter is accompanied by a preliminary report on the Mollusca, obtained during the cruise of the Blake by Mr. W. H. Dall.

Some of the apparatus used on the Blake is described with the aid of illustrations. Capt. Sigsbee's water bottle for collecting samples of sea water at various depths, is a very ingenious arrangement, and it has worked well in practice. The improved forms of dredge and trawl are also described.

The wire rope used for dredging and other purposes has proved very satisfactory, and Prof. Agassiz now recommends it for all future work of this character.

THE NATIONAL MICROSCOPICAL CONGRESS. THE first Congress of microscopists ever held in this country met last August, at Indianapolis, Indiana, at which time there were over fifty delegates present. The comparatively small attendance was, in great part, owing to the slight reductions in fare offered by the railroad companies, and to the delay in issuing the final circular by the local committee. Forty-nine names were registered, however.

Much interest was manifested by all who attended, and many went with the understanding that there was to be a permanent organization effected. Accordingly, a committee of delegates was appointed to consider the proper course to pursue in this matter, and on the last day of the meeting a provisional constitution was adopted, and the "American Society of Microscopists" came into existence. How many members of the Congress joined this society we do not know. The meetings are to be held annually at such places as may be chosen each year; the next one is to be at Buffalo, during August, 1879.

The officers of the Society are the following:

Dr. R. H. Ward, president; Dr. S. W. Dennis and C. M. Vorce, vice-presidents; Dr. Henry Jameson, Indianapolis, Ind., secretary; and H. F. Atwood, treasurer. These officers,

together with Drs. Geo. E. Blackham, J. Edwards Smith. and Wm. H. Atkinson, constitute for this year the committee on publications.

We wish the new society the best success, and trust that the Buffalo meeting will show that there is sufficient enterprise and enthusiasm to ensure its future well-being.

To return to the proceedings of the Congress we will give a brief account of each day's programme.

On Wednesday, Aug. 14th, the Congress assembled at the court house soon after ten o'clock. Rev. A. B. Hervey, of Troy, was made temporary chairman, and Mr. H. F. Atwood, of Chicago, secretary. Proceedings were then opened by a prayer, when Mayor Caven delivered an address of welcome on behalf of the city, and Dr. Orpheus Evarts followed with a similar one on the part of the scientists who had called the meeting. Dr. Evarts's address was in every way appropriate to the occasion.

The chairman responded briefly, and a committee was at once appointed to nominate permanent officers for the Congress. The officers thus nominated and elected were: Dr. R. H. Ward, president; Prof. J. E. Smith, and Dr. W. W. Butterfield, vice-presidents; H. F. Atwood, Chicago, secretary; and Dr. J. B. Marvin, of Louisville, treasurer.

The reading of papers began at once after this election. The first one was read by the secretary, as the writer, Prof. W. A. Rogers, was not at the meeting. The subject of Prof. Rogers's paper was:

THE LIMIT OF ACCURACY IN MEASUREMENT WITH THE MICRO

"" SCOPE.

This paper was quite elaborate, and embraced the results of experiments in measuring minute spaces in tabular form. For the most part the figures of Prof. Morley were compared with those obtained by the author, both measuring the same lines independently.

The results are summed up by Prof. Rogers, as follows: "1. Two equally skillful observers can measure the same space within about one-300,000th of an inch if the space does not exceed one-500th of an inch. For a space of one-100th of an inch, the deviation will probably amount to one-80,000th of an inch in case the measurements are made with an eye-piece or a filar micrometer.

2. The average deviation for accumulated errors, under similar condi

tions, is not far from one-50,000th of an inch for eleven intervals. For a large number of intervals the deviation will be somewhat larger, but it will not be proportional to the number of intervals.

3. A single observer can obtain an agreement with a normal equation representing all the observed values, as far as a solution by least squares can represent them, within somewhat smaller limits than those obtained by comparing the results obtained by two different observers. A paper was then read from Mr. C. C. Merriman, of Rochester, entitled

66 SOME NEW FORMS OF MOUNTING."

Shellac cement is the favorite with the author for making cells, either for dry objects or for such as are to be mounted in balsam in a cell. Anilin colors are used for ornamenting in preference to all others. One method of mounting, which gives fine results with certain objects, deserves notice, and we give it in the author's words.

"If the objects to be mounted will bear immersion in balsam, as shells, plant seeds, minerals, etc., I pursue the following plan: The thin glass covers are cemented to some old slips, which are kept for the purpose, by two or three touches of balsam applied at the edge of the cover. Care is taken in this, and in all cases, to accurately center all work on the slides by means of the self-centering turn-table. Then, on a light coating of balsam in the center of the cover, the objects, whatever they may be, are placed and arranged. When quite dry, and the objects are thus securely fastened, they may be completely covered by balsam and put into the dry-oven until thoroughly hardened. Then over the balsam Brunswick black, if the objects are white, or white zinc cement, if they are dark or high-colored, may be spread by thin layers at first, each being dried in the open air for a day before the next is applied, until there is no opaque covering to the objects. The thin glass cover is now thoroughly cleaned around the objects and then removed from the slips by a slight heating just sufficient to loosen it. It can then be turned over and mounted on the cell designed for it. The best preparation for fastening the cover to the cell is gelatine dissolved in water, with enough alcohol added to liquefy it from the jelly state. Just enough of the water cement seems to run in under the glass, and to dry just where it is placed. Afterward the cell may be finished with liquid balsam, carefully avoiding the little aperture, and the outer edge gathered up into a neat, trim little circle with the point of a knife on the turn-table."

This method of mounting in balsam on the cover, and backing up with black varnish, deserves to be better known. We have seen some of Mr. Merriman's slides made in this way,

and with certain objects such as the Orbiculina and Orbitolites, or Peneropolis from Bermuda sand, there is no method equal to

it.

The afternoon session was given up to the exhibition of instruments and apparatus.

The subject discussed on Thursday was principally angular aperture. Mr. W. H. Bulloch, of Chicago, made some pointed remarks upon the

FORMULAE OF OBJECTIVES."

He had some carefully-made drawings, showing the exact course of the rays through several objectives which have occasioned some discussion in the English journals.

Dr. Geo. E. Blackham followed with a long, but interesting paper on

ANGULAR APERTURE,"

which, owing to the nature of the subject, is too lengthy for our columns.

Mr. C. M. Vorce took up the remaining time in the forenoon with a paper on

66 MECHANICAL FINGERS."

In the afternoon Mr. R. Hitchcock read a paper on

"ANGULAR APERTURE DEFINED,"

an abstract of which appears in another place.

After the reading of this paper, Dr. R. H. Ward gave an account of his study of the ashes of leaves. This subject has already attracted considerable attention, and we may expect to hear more from it. Dr. Ward considers it to be of no little importance in vegetable histology.

Rev. A. B. Hervey then spoke for a few minutes about the 66 CLASSIFICATION OF ALGAE."

Our next number will contain a more complete paper on this subject.

As all the papers of the day were read, debate was in order. Mr. Hitchcock then introduced the following resolutions : WHEREAS, the subject of the angular aperture of objectives has been discussed for many years without great benefit to science, or showing even now a fair prospect of satisfactory solution;

WHEREAS, we believe that much of this discussion has sprung from the undefined meaning of the term; and

WHEREAS, we, representing in this National Microscopical Congress the various societies and classes of microscopists in the United States,