MR. NICHOLS.-Do I understand you to say you do not understand the reason for the intermittent flow of springs?

MR. BLISS.-No, I am sorry to say I do not.

MR. NICHOLS.-I do not know that I do either, but when I was a boy, I used to think it was the syphon effect of a syphon outlet.

MR. BLISS.-Take a place where it varies with the time-I do not mean the intermittent time where it would gradually decrease for several days and then increase again, for we have geysers that increase for a certain length of time and then decrease, and perhaps stop altogether for a while.

MR. NICHOLS.—That was on account of the syphon principle which the discharge of a spring has, going up and down in the form of a syphon; as the reservoir filled it to the top it started to run over, and when it discharged to a point where the air was admitted, it would stop and permit the reservoir to fill up again MR. BLISS.-I see, thank you.

MR. CHEYNEY.-The Conemaugh River at the time referred to was extremely low and the water was very shallow. The stream bed was filled with stones and boulders which projected above the water surface; probably 50% of these boulders being exposed to the air. The direct rays of the sun upon these boulders in the shallow stream undoubtedly raised the water temperature to a comparatively high point, and the evaporation was no doubt very great on this account.

MR. W. P. DALLETT.-This same action is seen in wells that flow. I have seen a hydraulic ram operating on a well in Camden getting its water under pressure from an artesian well, and at times of new and full moon we find the pressure falling off and decreasing during the day in rhythm with the tide-not exactly the same time as the tide, but in rhythm with it, and at other times of the month the operation is very much less.

PAPER NO. 1120

STEREO PHOTO SURVEYING

By HENRY HESS

Read February 1, 1913

Certain work that I was engaged in some time ago developed the need of special optical apparatus, the design of which took me to Jena, to the famous Zeiss concern. Dr. Pulferich, the Chief of a certain section, showed me some apparatus that will, I believe, be of interest to all of you, and possibly more particularly to the civil engineers and architects among you.

Would you be interested to know that you could take two stereoscopic photographs of a building from diagonally opposite diagonal viewpoints and then from these, in the quietude of your office, construct as correct a ground plan as would be possible to you with the most careful work in the field?

Who among you has enjoyed the experience of making surveys in heat and cold, in rough, broken and most difficult country? Would you call it a pipe dream were it suggested that all you needed was a camera, and that you could do most accurate plotting at your convenience and with every comfort in your office from the photographs taken in the field? And that you could devote the open season to photographing every possible territory for, say a projected railway, and then pick out the best from plottings made in your office?

And if you would call that a pipe dream, what would you say of a person who suggested that you could take photographs from mountain tops and balloons and save yourself all the troubles of climbing

over hills and through valleys, but instead sit comfortably n your office over your photographs and special apparatus and not only plot out your contours, but easily prove for correctness from a complete new set of observations without moving out of your office?

Some of you are more or less interested in affairs astronomical. What do you say to using sim lar apparatus for plotting and sur

veying the heavens, measuring star movements and checking astro-
nomical calculations by relatively simple apparatus?

Coming back to earth again, what do you think of an application
of the same apparatus adapted to automatic portrait sculpture?
But enough of questions! Results are what you want!

This first picture is what the Zeiss people euphoniously (Fig. 1)

The Weather Bureau data comprise not only the ordinary records of temperature, precipitation, wind, and sunshine, but also include gauge records of all the principal streams. These river gauge records are indispensable in calculating the run off for a given drainage area, or for determining its relation to the precipitation. During the last few years the Bureau has maintained a large number of special snowfall stations in mountain districts of the far West, and thus reliable information is furnished regarding the reserve water supply for many power plants and irrigation operations.

In closing I wish to express my belief that in the future the hydroelectric and the agricultural engineers are to become the leaders of the profession, the opportunities of the agricultural engineer being practically unlimited. Their efficiency will depend, in no small measure, upon their ability to make intelligent use of meteorological data in their computations.

DISCUSSION

MR. JOHN C. TRAUTWINE, JR.-I need hardly remark that Mr. Bliss is entirely mistaken in saying that one of the chief merits of his paper was its brevity. It might well have been much longer.

The activities of the Weather Bureau admirably illustrate the fact that not only can the Government do some things better than the individual or a private corporation, but it does things which no individual, firm or corporation would undertake, because there is no money in them."

If I understand Mr. Bliss correctly, the complete records for each district are sold on subscription (and I venture to say that the fee is very moderate) while the separates can be had for the asking.

I know of no one who is better qualified to discuss this question than our veteran fellow-member, Mr. Codman, to whom we are indebted for many years of hard, painstaking and intelligent work in charge of the city's gauging stations, and for the city's success in wheedling, out of the City Councils, the paltry sums required to keep these stations going.

MR. CODMAN. For the past twenty-nine years, the Bureau of Water, Department of Public Works, has maintained a series of observations on rainfall and stream flow, and have secured valuable data on a number of streams in this vicinity, including the Schuylkill River.

A discussion of the whole subject of rainfall and stream flow in connection with the value of meteorological observations to the engineer would consume much more time than is usually allowed in discussing the main topic of the paper. I will, therefore, confine my remarks to the collection of the rainfall data and its value in computing its sequence in the amount found flowing off in the natural water courses and drainage from the surface of the ground.