1898-1902. No. 4.] ASTRON. AND GEODET. OBSERVATIONS. 3 



5. A compass. The card (Thomson's) was one taken out of an 

 ordinary mariners' compass, and placed in a box made on board. 



6. A Negretti & Zambra telescope, with an aperture of 7.4 cm. 

 and a magnifying power of 65 diameters. This was used for the ob- 

 servations of the solar eclipse of the 28th May, 1900. 



7. Three odometers were made during the voyage, the first during 

 the winter 1898—99. I made a trial of this in the spring of 1899, and 

 found it very useful on an expedition across EUesmere Land in the 

 summer of that year. As it proved an excellent contrivance in surveying, 

 two more were made later on. 



An odometer is a wheel, to the axis of which is attached a regis- 

 tering-apparatus, which records the number of revolutions performed 

 by the wheel. When the circumference of the wheel is known, the 

 distance traversed may be calculated. 



The relative proportions of the radius of the wheel and the gearing 

 of the registering-apparatus were so arranged that the distance traversed 

 could be read off directly from the latter. (See PI. I and II.) 



The registering-apparatus consisted of three endless screws, which 

 geared into three corresponding cog-wheels. 



Screw No. 1, which was firmly attached to the axle of the wheel, 

 imparted motion to screw No. 2 in 22 revolutions. Screw No. 2 in its 

 turn transmitted motion to screw No. 3 in 36 revolutions. Thus from 

 axle No. 1 to axle No. 3, the number of revolutions was 792. The 

 circumference of the wheel measured 2.341 metres, and therefore in one 

 revolution of axle No. 3, the wheel covered a distance of 2.341 metres 

 X 792 = 1854 metres = 1 nautical mile. 



Axle No. 3 was furnished with an index, moving on a dial that 

 was divided into tenths of a nautical mile. Hundredths of a mile could 

 be judged. 



In order to count the whole number of miles, screw No. 4 trans- 

 mitted motion to axle No. 4 in 30 revolutions. The index of axle No. 

 4 thus registered up to 30 nautical miles. 



The principle itself is well known and of general npphcation on 

 bicycles and carriages. The difficulty in our case was to obtain a 

 practical connection between sledge and wheel, and to make it sufficiently 

 strong and light. 



In order that it might be used under varied conditions, the wheel, 

 when connected with the sledge, had to be capable of being moved up, 

 and down, and to the sides, in relation to the sledge; and all the time 

 it must remain upright. 



