Man's physical universe

xanabras

11 THE UNIVERSE A VAST SYSTEM OF PARTS

The Temperature of Stars May Be Measured by Several Other Instruments.

5. B. Nicholson and Edison Pittit adapted a simple instrument called

the "thermocouple" to the measurement of the temperatures of the

different stars. If one of two strips of different metals held in contact

with each other is heated, an electric current is produced. The astronomer's

thermocouple consists of a minute wire of bismuth and a similar

wire of a bismuth alloy containing five per cent tin, joined at their

extremities and fastened to a blackened receiver in order to absorb

the maximum amount of light from a star. The heat produced by

these light rays produces a feeble electric current which is measured

with a sensitive current-measuring device called a "galvanometer."

A somewhat similar instrument, the bolometer, was invented by

5. P. Langley. It consists of two very fine wires of platinum about

1/2500 of an inch in diameter, mounted in a constant-temperature

chamber in such a position that light will strike one wire but not the

other. The difference in the electrical resistances of the two wires can

then be measured with sufficient accuracy to indicate less than

1/1,000,000 degree rise in temperature.

C. G. Abbott has invented the most sensitive heat-measurer known,

the kampometer. Its sensitivity exceeds that of the thermocouple or

the bolometer, from which it differs in principle.

It utilizes the principle

that two metals expand unequally when they are heated.

The scientific significance of these different instruments for measuring

the temperatures of the stars is

that they permit the scientist to

check his results by different methods, using different instruments,

and thus make his observations more reliable.

The Stellar Interferometer Is Used to Measure the Diameters of Stars.

The stellar interferometer was invented by Albert A. Michelson

(1852-1931). One such interferometer, used at Mount Wilson, can

measure the angle made by a star's disk which is about equal to that

filled by the head of an ordinary pin when placed in Boston and observed

from New York.

These Instnmients Have Given Man a Picture of Our Galaxy.

Number of Stars.

F. G. Pease (1881-1938) estimated the number of

stars in out galaxy to be between thirty and forty billion. Other

astronomers have given estimates as low as one billion. There are no

estimates today that are considered to be reliable.

Arrangement of the Stars. The stars in our galaxy seem to be

arranged in the form of a huge watch, the thickness being variously

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