The principles involved in obtaining successful photographs with the microscope are the following:

1. To use objectives so corrected as to bring the actinic ray to a focus.

2. To illuminate by direct sunlight passed through a solution of ammonio-sulphate of copper, which excludes practically all but the actinic extremity of the spectrum.

3. Where it is desired to increase the power of any objective, to use a properly constructed achromatic concave instead of an eye-piece.

4. To focus on plate glass with a focusing glass, instead of ground glass.

5. With high powers to use a heliostat to preserve steady illumination.

6. Where an object exhibits interference phenomena when illuminated with parallel rays, as is the case with certain diatoms and many of the soft tissues, to produce a proper diffusion of the rays by interposition of one or more plates of ground glass in the illuminating pencil.

Strict adherence to these principles is indispensable to success. In the Museum they have been carried out by the following details:

A camera is not used, a dark room being found most convenient. The operating room has two windows, through one of which just enough yellow light is admitted to permit the movements of the operator. The lower part of the other window is occupied by a shutter about fourteen inches high on which the blackened sash shuts down light-tight. In this shutter is a round hole an inch and a half in diameter, from the inner side of which a brass tube of the same diameter projects into the room. On the outer side of the hole is a rod about twelve inches long, on the extremity of which the microscope mirror is duly centered. Two steel rods attached by hooks to the mirror and passed through the shutter permit its position to be adjusted by a person standing inside of the room, without opening the window. A Silbermann's heliostat standing on a shelf just outside of the window throws the sunlight steadily upon the mirror. Within the room a frame of walnut, ten feet long, is placed on a firm table perpendicular to the window. The microscope stands on the end of this frame next the window, its mirror is removed, being replaced by that outside the shutter. The microscope is placed in a horizontal position, and the tube carrying the diaphragm or the achromatic condenser fits into the tube projecting inward from the shutter by which the sun's light reflected from the mirror outside is admitted. A black velvet hood covers the parts about the stage and objective of the microscope, and thus prevents the leakage of light into the room.

The plate holder is movable backward and forward on the walnut frame on which the microscope stands, its maximum distance from the stage of the microscope being nearly nine feet.

To permit ready focusing at distances greater than the length of the arm, a wooden rod ths of an inch in diameter and capable of easy rotation runs the whole length of the right side of the frame. The milled head of the fine adjustment of the microscope is grooved, and a small grooved wheel in the end of the rod permits the two to be connected with a band. The operator standing at any part of the frame can therefore manipulate the fine adjustment by simply turning the wooden rod in his fingers. The arrangements of light, position of object, coarse adjustment, &c., are made by the operator, who stands by the microscope, which has a suitable eye-piece adjusted, and observes the object in the usual way; afterwards, removing the eye-piece and going to the plate holder, the final focusing is made by means of the wooden rod, the image being viewed with a focusing glass on a piece of plate glass held in the same frame which is to receive the sensitive plate.

The cell containing the ammonio-sulphate of copper hangs outside the shutter over the hole by which light is admitted. It not only excludes the unnecessary illuminating rays, but prevents danger to the objective from the concentrated solar heat and permits the eye of the operator to view the objects about to be copied without fatigue or injury. Latterly a plate of alum has also been used to exclude solar heat especially during any temporary removal of the ammonio-sulphate cell. The chemical processes employed are well known to all photographers. With the above apparatus, it has been found that the best defined pictures are obtained when the distance employed with any objective does not exceed three or four feet.

The achromatic concave used as a substitute for the eye-piece is a combination of somewhat more than half an inch transverse diameter, and about 28° angle, constructed, like the objective, to focus the chemical rays. It increases the magnifying powers of the objective about seven times. It has been found to perform well with both the 4th and th.

In photographing the soft tissues or other objects in which illumination with parallel rays produces interference lines, the ground glass is to be placed between the mirror and condenser. Of course, there is considerable diminution of light, but this can be overcome, for the higher powers, by condensing the sun's light on the ground glass by a bulls-eye or other similar contrivIf the interference lines as seen by the eye do not disappear with one thickness of ground glass, two or more may be used.

ance.

The most powerful objective with which photographs have

been taken in the Army Medical Museum is a 'th, manufactured recently for the Museum by Messrs. Powell and Lealand of London. The subject selected for the experiment was Pleurosigma angulatum. With the 'th and three feet nine inches distance and without an eye-piece, a picture of a portion of a frustule was obtained magnified 2,344 diameters. This negative readily bore enlargement to 19,050 diameters. The field in the picture is six inches in diameter and is remarkably sharp in the center, but shows considerable curvature and on the edges is quite out of focus. Further experiments with the 'th satisfied us that a greater power could not be advantageously obtained from it.

About the same time experiments were made with the Wales' th, due amplification being given by the achromatic concave. It was intended to obtain with this the same power as with the 'th, but, although the distance was reduced to 3 feet, the subsequent measurements showed 2,540 diameters, or about 200 diameters more than were obtained with the 'th. This was the maximum performance of the 4th and readily bore amplification to 19,050 diameters. The field thus obtained with the 4th, over seven inches in diameter, was absolutely flat. I send you herewith albumen prints of both sets of pictures. You will observe that the small pictures with the 'th are the sharpest, owing in our opinion to somewhat better chemistry in making the nega tive, while, of the enlargements, that from the 4th picture is best, owing to the greater flatness of the field in the original negative.

Without going into a discussion of the comparative merits of Powell and Lealand's 'th in this place, it is interesting to ob. serve that these photographs confirm the opinion expressed by Prof. Rood in this Journal' as to the circular nature of the markings on Pleurosigma angulatum, an opinion which had previously been expressed by Mr. Wenham.

At the date of publication of Circular No. 6, Surgeon General's Office, both Dr. Curtis and myself believed these markings to be hexagonal, as was stated and figured on page 148 of that work. The greater power now obtained has corrected this opinion, but it is worthy of note that in the present pictures the markings appear hexagonal in both the small ones, if viewed with the eye at the visual distance, while on close inspection or with a lens they are seen to be circular. In the pictures with 19,050 diameters the circular shape of the markings is very plain, but if viewed from a considerable distance or with a concave lens, they appear hexagonal. I also send you herewith a photograph of cartilage magnified 370 diameters, in illustration of the results attainable in the photography of the soft tissues. This

On the evidence furnished by Photography as to the nature of the markings on the Pleurosigma angulatum; by Prof. O. N. Rood, this Journal, vol. xxxii, p. 335.

picture shows capsules, corpuscles and nuclei with the utmost sharpness.

In short, it is our opinion that henceforward photography is indispensable to the proper representation of microscopic objects, and is, as practised in the Army Medical Museum, even in its present condition, adequate to the satisfactory representation of all microscopic objects that do not depend for their value on colors.

ART. XXVII.-Note on a Regular Dimerous Flower of Cypripedium candidum; by ASA GRAY.

Mr. J. A. Paine, Jr., of New York, who two years ago detected an interesting monstrosity of Pogonia ophioglossoides, has now brought to me, preserved in spirit, a monstrous blossom of Cypripedium candidum, which demands a record.

The plant bears two flowers: the axillary one is normal; the terminal one exhibits the following peculiarities. The lower part of the bract forms a sheath which encloses the ovary. The labellum is wanting; and there are two sterile stamens, the supernumerary one being opposite the other, i. e., on the side of the style where the labellum belongs. Accordingly the first impression would be that the labellum is here transformed into a sterile stamen. The latter, however, agrees with the normal sterile stamen in its insertion as well as in shape, being equally adnate to the base of the style. Moreover the anteposed sepal is exactly like the other, has a good midrib and an entire point. As the two sterile stamens are anteposed to the two sepals, so are the two fertile stamens to the two petals, and the latter are adnate to the style a little higher than the former. The style is longer than usual, is straight and erect; the broad, disciform stigma therefore faces upwards; it is oval and symmetrical, and a light groove across its middle shows it to be dimerous. The placentæ, accordingly, are only two. The groove on the stigma and the placenta are in line with the fertile stamens.

Here, therefore, is a symmetrical and complete, regular, but dimerous orchideous flower, the first verticil of stamens not antheriferous, the second antheriferous, the carpels alternate with these; and here we have clear (and perhaps the first direct) demonstration that the orchideous type of flower has two stamineal verticils, as Brown always insisted.

ART. XXVIII.-Contributions from the Sheffield Laboratory of Yale College.-XII. Analysis of a Mineral Water; by FREDERICK F. THOMAS, Ph.B.

THE mineral spring, the water of which is the subject of this notice, is situated in the town of Barton, Tioga Co., New York, about seven miles northeast of the village of Waverly, near what is called Talmadge Hill. It is one of two sulphur springs that have been observed in that county. The other, resembling it in character, is about twenty miles north, near the village of Spencer; both have been noticed in the State geological reports, and have been in repute for many years among the inhabitants of that region on account of certain remedial properties which their waters are supposed to possess.

This spring rises from rocks of the Devonian age-the blue argillaceous shale and sandstone of the Chemung group-of which many outcroppings may be seen in the immediate neighborhood of the spring. These rocks, according to examinations made in this Laboratory, consist principally of silicate of alumina, but also contain sulphuric acid, lime and magnesia in considerable quantities, some potash, soda and iron, as well as chlorine, organic matter, and a trace of manganese. They turn black upon heating before the blowpipe, but no effervescence is observed on treating them, in the pulverized state, with acids. The water partakes considerably in its mineral character of the properties of the rocks at the surface, but contains a very small amount of sulphates, while a large percentage of its mineral constituents are carbonates. The mean of two corresponding determinations of sulphuric acid made on the water as soon as received at the laboratory, gave 0-116 grain per gallon, while other estimations, made from water which had remained sealed in bottles for some weeks, gave a slightly larger amount, which resulted from oxydation of sulphur.

As the rocks in which the spring rises contain traces of manganese, that substance would probably be found in the water, were a large amount concentrated. None was however detected in the quantity of water at disposal.

The sulphur and sulphuretted hydrogen in the water may be due to the reduction of sulphates by organic matter and the subquent liberation of sulphuretted hydrogen by free carbonic acid.

The comparatively small amount of sulphates in the water, the presence of organic matter in the rocks, the temperature of the water, which is quite low, would be in support of this view; as well as the fact that none of the surface rocks appear to contain sulphids-quite a large excavation having been made in the immediate vicinity without revealing any pyrites.