moment we can free our minds of local time and the association of the _same hour_ with the _same portion_ of the day at _all places_. The great interest at present manifested in the attempts to reach the North Pole calls for some consideration of universal time in the extreme north. Commencing at the equator, it is easy to see that the day and night ring, Fig. 46, would represent the days and nights of 12 hours at all seasons. As we go north, however, this ring represents the _average_ day and night. When we reach the Polar Circle, still going north, the _daily_ rising and setting of the sun gradually ceases till we reach the great one-year day at the Pole, consisting of six months darkness and six months light. Let us now assume that an astronomical observatory is established here and the great equatorial placed precisely on the pole. At this point, _local time_, _day and night_, and _the date line_, almost cease to have a meaning. For this very reason universal time would be the only practical method; therefore, it _more_ than stands the test of being carried to the extreme. Universal time would regulate working and sleeping here the same as at all other places. Strictly local time in this observatory would be an absurdity, because in walking around the telescope (pole) you would be in all instants of the 24 hours within five seconds! At the pole the day would commence at the same instant as at some assumed place, and the day and night ring would represent working and sleeping as at that place. Suppose this observatory to be in telegraphic communication with New York, then it would be best for the attendants to set their day and night to New York, so as to correspond with its business hours. Many curious suppositions might be made about this polar observatory with its "great night" and equally "great day." It is evident that to keep count of itself it would be compelled to note _dates_ and 24-hour _days_ to keep in touch with us; so it would be forced to adopt the local day of some place like New York. This choice would be free, because a polar observatory would stand on all the meridians of the earth at once.