Première page Page précédente
Page suivante Dernière page Illustration précédente Illustration suivante Réduire l’image 120% Agrandir l’image Revenir à la taille normale de l’image Rotation antihoraire 90° Rotation horaire 90° Imprimer la page
Basculer à gauche  Basculer à droite

205

altitude scale are so arranged that with a scale extending up to 3,000 metres, differences as small as two metres can be read without the use of a vernier. The aneroid is read and set without removing it from its case, and the altitude scale automatically locks so that it cannot get shifted during transit. A small swing thermometer, for ascertaining the air temperature, is carried in the pocket at the back of the case. The altitude scale of the aneroid being computed for the weight of air at a given temperature which is noted on the dial of the instrument, a simple correction should be made, when the temperature at the time of observation differs from this value ; printed instructions for doing this are attached to the leather case. The diameter of the dial is 82 mm. which admits of an open scale.

12. Barograph.

A self-recording aneroid barometer, giving a continuous record of atmospheric pressure. The instrument consists of an aneroid movement, which is multiplied by a system of levers, and communicated to the pen which traces an ink line on the chart.

13. Luminous Magnetic Compasses. (Fig. 8.)

These compasses have been designed more particularly for military purposes. The dials and direction pointers are coated with a preparation, which on exposure to a bright light becomes luminous. The luminosity is retained for some hour’s, and is sufficiently brilliant to enable a person to march on a bearing at night time, and at the same time is not brilliant enough to betray his position. The mechanical construction permits bearings to be observed by day or night. Two sights are sometimes attached to the compass and serve for taking bearings, and for rapid field sketching. Fig. 9 illustrates a luminous magnetic compass fitted with a prismatic back-sight and a line fore-sight.

Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 99,94 %.

La langue de reconnaissance de l'OCR est l'Anglais.