288 THENORTHPOLE 



words in my diary: "The Pole at last. The prize of 

 three centuries. My dream and goal for twenty years. 

 Mine at last! I cannot bring myself to realize it. It 

 seems all so simple and commonplace." 



Everything was in readiness for an observation 1 at 



1 The instruments used in taking observations for latitude may be either a 

 sextant and an artificial horizon, or a small theodolite. Both these instruments 

 were taken on the sledge journey; but the theodolite was not used, owing to the 

 low altitude of the sun. Had the expedition been delayed on the return until May 

 or June, the theodolite would then have been of value in determining position and 

 variation of the compass. 



The method of taking meridian observations with a sextant and an artificial 

 horizon on a polar sledge journey is as follows: if there is any wind, a semicircular 

 wind-guard of snow blocks, two tiers high, is put up, opening to the south. If 

 there is no wind, this is not necessary. 



The instrument box is firmly bedded in the snow, which is packed down to a 

 firm bearing and snow is packed around the box. Then something, usually a 

 skin, is thrown over the snow, partly to prevent any possible warmth from the sun 

 melting the snow and shifting the bearing of the box; partly to protect the eyes 

 of the observer from the intense reflected glare of light from the snow. 



The mercury trough of the artificial horizon is placed on top of the level box, 

 and the mercury, which has been thoroughly warmed in the igloo, is poured into 

 the trough until it is full. In the case of the special wooden trough devised and 

 used on the last expedition, it was possible to bring the surface of the mercury 

 level with the edges of the trough, thus enabling us to read angles very close to 

 the horizon. 



The mercury trough is covered with what is called the roof — a metal frame- 

 work carrying two pieces of very accurately ground glass, set inclined, like the 

 opposite sides of the roof of a house. The object of this roof is to prevent any 

 slightest breath of wind disturbing the surface of the mercury and so distorting 

 the sun's image in it, and also to keep out any fine snow or frost crystals that 

 may be in the atmosphere. In placing the trough and the roof on the top of the 

 instrument box, the trough is placed so that its longer diameter will be directed 

 toward the sun. 



A skin is then thrown down on the snow close to the box and north of it, 

 and the observer lies down flat on his stomach on this, with his head to the south, 

 and head and sextant close to the artificial horizon. He rests both elbows on the 

 snow, holding the sextant firmly in both hands, and moving his head and the 

 instrument until the image or part of the image of the sun is seen reflected on 

 the surface of the mercury. 



The principle on which the latitude of the observer is obtained from the alti- 

 tude of the sun at noon is very simple. It is this : that the latitude of the observer 



