the up-grade, and that the river is more or less returning to its earlier state. We have a striking example of the recent changes in the case of Lake Malombe. Two years ago the lake was completely dry at the end of the dry season; I walked right across it and it was not even swampy. But from the head of the lake right up to Lake Nyasa there was a continuous stretch of water, and as far as one could judge the water in the river stood above the floor of Lake Malombe; it was held up by what in navigation times was known as the Nelicoli Bar. It appeared that if Lake Nyasa rose just a little more, just sufficient to overtop that bar, then Malombe would be flooded and would become a lake once more. Within two or three months the rainy season began, and the lake rose more and more until it overflowed that barrier, and since then Lake Malombe, after many years, has been fully re-established. If the view as to the periodical variation of the lake-level is correct, the lake will continue to rise for another one or two years.

The older lacustrine deposits are known only at the northern end of Lake Nyasa, and the southward extension of the lake is proved by the successive deposition of the younger deposits farther and farther in this direction.

In conclusion, I would like to express my thanks for the very appreciative remarks made by the different speakers, as well as for the manner in which the paper has been received.

The PRESIDENT: I hope Dr. Dixey will accept our best thanks for a very able and clear discourse upon a subject which has obviously many aspects, and very considerable and different interests—such as the question of the rise of level of the lake and the economic consequences which may follow its variations, the question of railways and population, and that other question which no one has touched upon, namely, the dinosaur bone deposits. However, that will perhaps come up again early in the next session, when we hope to hear something about dinosaur deposits in another continent. I am sure you will express your thanks to Dr. Dixey in the usual way.

PHOTOGRAPHY ON THE HAMILTON RICE
EXPEDITION, 1924-25

From the Report prepared at the direction of Dr. Hamilton Rice for Major-General Mason M. Patrick, Chief of Air Service, U.S. Army, by Capt. A. W. Stevens, U.S. Air Service.

QUIPMENT.-The Hamilton Rice Expedition brought from the United States the following apparatus :

1 Fairchild Aerial Camera, 12-inch focus, same as U.S. Air Service model K-3. Complete with extra magazine, mount, and carrying cases. 1 Fairchild Aerial Camera, 20-inch focus, same as U.S. Air Service model K-6 for oblique photography. Complete with view-finder and 3 filters, X 12 Minus Blue, K-3, and Aero 1; 16 rolls of Eastman Hypersensitized Panchromatic Aerial Film.

I Bell & Howell Motion Picture camera and tripod; lenses, 2 inch, 3 inch and 6 inch.

1 Graflex Camera, 31 x 41 inches, revolving back, long focus, with

plate, cut film, and roll film holders. Lens, convertible anastigmat, 6 inch and 11 inch.

I Kodak, 3 × 5 inches, using roll film.

1 View Camera, 5 × 7 inches, using plates. Lens, convertible, 7 inch and 12 inch.

1 Eastman Kodak Co. Developing Machine for Aerial Film, complete with tanks, assortment of trays, and chemicals; printing frame, scales, thermometers, timing clock, Velox and Azo printing paper, etc.

Filters. The same ray filters used on the 20-inch camera were used on the 12-inch camera, by fitting a bayonet socket at the end of the 12-inch cone. This saved having a duplicate set of filters, and worked perfectly. For vertical photographs the K-3 filter was used most, from the comparatively low altitude of 6200 feet. At higher altitudes the X 12 would have been necessary. All three filters were used for oblique photography, depending on the distance of the subject to be photographed. For extremely distant views the X 12 is used; for medium distance the K-3; for objects comparatively close, the Aero 1. On cloudy days, or in very early morning or late evening, the lens was used without a filter.

Sensitized Materials.-No trouble was experienced in using any of the photographic materials in this climate. The absence of ice made it necessary to carry out all operations at the prevailing river temperatures, which varied between 80° and 85° F. Standard chemicals, of the kind regularly purchased by the U.S. Air Service, were used, and although special chemicals, such as formaldehyde, were brought along, it was unnecessary to use them.

Development.-All the development work was done at night, in a tent provided for the purpose, or in a thatched shelter covered with a canvas tarpaulin. At first the water for the solution was set out in discarded gasoline tins and other basins to cool as evening came, and work was started at 3.00 a.m. When daylight came the film was ready for hanging up to dry. Water left in the open at night will cool about 5° below river temperature. As work progressed it was found that it could be carried out nearly as well immediately after nightfall, at river temperature. Hand electric flash lamps and kerosene lanterns were used when light was needed. Tropical moonlight is often very bright, and although the tent openings were carefully closed, it was often light enough inside the tent to make out the silhouettes of all objects plainly. The canvas was of the copper-treated, mildew-proof kind, and exercised a filter action, insomuch that the light admitted was a very pale green; tests showed that moonlight, filtered through the tent, had no appreciable fogging action on ordinary plates or film. With the panchromatic film no chances were taken, and work was carried on either before moonrise or after the moon had gone down.

Aerial Film. The Aerial Panchromatic Film, hypersensitized, kept

surprisingly well, to work free from fog as late as April 1925, or eleven months after manufacture; it had been at 85° F. most of this time. It is important, if film cannot be kept cool, that it be kept at least at a uniform temperature, and particularly that the tin, or even the outer cardboard container, be not exposed to the direct heat of the sun. If the package gets hot, the film deteriorates at once. This applies to all photographic sensitized materials; aerial film, Kodak film, dry plates, and paper. If they cannot be kept cool, at least they must be kept from a temperature higher than that normal to the country.

Sensitized Paper. -No trouble was experienced with either Velox or Azo paper. Velox prints worked clean and white on the margins, with good blacks in the shadows. These prints underwent ferrotyping successfully and did not stick to the ferrotype plates. Velox has one peculiarity that often causes it to be condemned by workers who are not fully acquainted with it. In damp climates this paper absorbs a certain amount of moisture from the air, and it is apt to absorb it unequally or in patches. When immersed in a normal developer, the surface of the print repels the solution in spots, much as if it were oiled, and the developed print then shows white streaks all over its surface. The remedy is very simple indeed: double the strength of the developer, that is, add less water to the stock solution; or, add several spoonsful of sodium carbonate, either crystals or powder, to the normal developer. In either case the increased alkalinity of solution will ensure even development, and the trouble from white streaks will cease.

Developer for Aerial Film.-Pyrogallic acid was used for developing the aerial film. Pyro is acknowledged to be the best developing agent for negatives; it is more messy and does not keep as well as other developers, but it produces negatives of the finest quality, and moreover develops with a minimum of chemical, which is a very important consideration. Furthermore, it is a comparatively inexpensive chemical, and a tank of developer used for one or two aerial rolls may be thrown away without great loss. Freshly mixed developer makes for more uniform results than a tank of better-keeping developer that is used over a long period of time, for a certain amount of bromide enters the developer with each batch of film treated, and this affects the character of the developer.

When aerial film was developed, it was usual to develop it and plates or small film on hand in the same tank of solution. If there was no aerial film to develop, and work on the smaller sizes was necessary, it was customary to use a diluted Metol Hydroquinone developer, in trays. Paper was always developed in the M.H. developer, in trays. The Pyro developer should be used only while it is fresh, within an hour, or at most a few hours, after mixing. If it has scum on it, this must be brushed or floated off before using. If the scum sheet is very thin, a vigorous stirring will suffice.