| Show STAR TIME rime AND SUN time the way astronomer find oat frova from the stars star when it Is noon the time for sending out the noon signal from washington Is the instant the sun ean crosses the seventy afif fifth th meridian this however is not the run which gives us light and beat but an invisible imaginary one because for foi certain reasons the true troa sun does not cross the meridian at the same moment every day but during one part of the year he be gets over it a little more ahead of time each day and during the other part he is correspondingly behind time and so this fictitious sun bun is used because its apparent path around the earth brings it exactly over the same line eno at the same moment every day now at just what instant this sun crosses the meridian is determined by means of the stars for time at the observatory is not reckoned by the sun son but by the stars every clear night an astronomer at the tha observatory looks through a large telescope for certain stars stara which he knows kno must cross acer acif iain tain line at certain times timea and by the sisa of electrical an machine he makes a record of the time each star passes as shown by a clock which keeps sidereal or star time he then consults it a printed table which shows him at just what time each star must have passed and by as much as this time differs from that recorded by the clock the latter is ia wrong and in that way the sidereal clock is ia regulated this star time is ia then reduced to sun time which requires some calculation as there is a difference between the two ol of about four minutes each day these two docks clocks the one keeping star time and the other su spa time ave are of very fine quality aud and are as near perfection as possible although they cannot help being affected by changes of temperature ant and different conditions of the atmosphere mo sphere they very rarely are more mora than a fractional part of a second out of the way no attempt is ever made to correct such errors but they are carefully noted and all allowed 0 wed for in making calculations calculations for the purpose of distributing time a third clock known jas a transmitter is ia used this is ia set to keep time by the seventy fifth meridian and is ia regulated by the standard clock before mentioned it is in all respects similar to the other clocks except that it has attached 0 0 it an ingenious device by which an electric circuit may be alternately opened and closed with each reach beat of the pendulum ia 11 home ome jour jona ual cal |
