Page:Popular Science Monthly Volume 89.djvu/881

 Popular Science Monthly

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��"This part of the dam has only recently been laid," said the engineer, "and the heat, generated chemically b\- the cement in the concrete as it solidified, has not passed off yet."

Then he explained that concrete expands and contracts, after the fashion of steel, and that the dam had been built in sections about seventy-nine feet long, interlocking from the bottom to the top. Observation of other Cyclopean structures of masonrj- had revealed the fact that in the course of expansion and contraction cracks appeared about se\"enty-ninc feet apart. So it had been decided to provide in this way for expansion-joints in the dam.

As little was known of the changes of temperature which occurred in a large mass of concrete and as this information might be of value in designing other structures of similar character, it was determined when the Kensico dam was built that its temperature should be taken regularly at different points between the base which is one hundred and fifty feet below the surface of the ground and the top, approximately the same distance above it. This has now been done for a period of more than two years, ,

an electric thermometer being used /^i': for the purpo.'ic.

A thermophone is a de\ice which will measure by means of an electric circuit the tempera- ture at any point connected with it by wires. Its principle is that of the well-known Wheat- stone bridge by which resist -

��ancescanbemeasured.Thecablc which leads from the recording apparatus and the dry batteries to the sensitive resistance coils where the temperature is to be taken carries three insulated wires. Through one of them the current passes to the sensitive terminal, where it is divided and returned through two minute coils of copper and German silver wire. These metals are affected differently by changes in temperature. These changes affect differently the free- dom with which a current of electricity will pass through them, and this difference in- dicate what the temi)erature is.

Forty-seven thermometers were buried in the dam, the lowest being below the founda- tion. They were connected with switch- boards placed at central points, the cables, carefully protected, being buried in the masonry as it rose. There are three switch- boards, the lowest being stationed in a nook in the long inspection-galler)\

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���Will the Great Sphinx Scowl When She Sees This? X seeing America first one should not ■ ivcrlnok the Sphinx built at Blue Point, Long Island, by William Graharq. This domestic Sphinx is just one seventh the size of the original great Sphinx in Egypt, and it !s just as mute. It weighs forty-two tons.

The idea of decorating his Iront yard with a copy of Egypt's great at- traction came to Mr. Graham when he was renuning a large quantity of sand from his lawn. In- stead of carting the sand away, as he had done in past years, he col- lected it in a huge pile, and then drew up plans for his Sphinx. The sand was mixed ^\ ith concrete and iron scrap. The head of Mr. Graham's jfi Sphinx is solid, weighing ten tons. ^^~*i* The lower part of the image has a circular chamber with an open- ing at the rear. Seats and pillars of concrete extend around its inner walls.

��The head of the Sphinx weighs ten tons. The lower part of the image is a room with an opening at the rear

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