Progress of Invention, 229 



magnetic meridian. A wire which is fixed in the centre of the 

 needle, and by the upper extremity of which it is suspended, carries 

 at its lower extremity another needle that is of copper, well 

 balanced, and having at one end a point which projects downwards. 

 This point is intended to mark the deflections of the magnetized 

 needle, produced by the thermo-electric current. For this pur- 

 pose there is placed under it horizontally an annular disc about two 

 inches in diameter, which carries a disc of paper, and is supported 

 on an upright rod, to which a regular movement of rotation is 

 imparted by clockwork, and which besides, at fixed intervals of a few 

 minutes, is made to ascend and descend vertically by means of a 

 cam. "When the disc of paper is raised it comes in contact with the 

 point which projects down from the copper needle, and is pierced by 

 it, since the copper needle is prevented from moving away by an 

 annular disc that is placed over it, and affords a support to it when 

 the paper and point come in contact. The redescent of the paper 

 disengages the point. Thus the deflections of the magnetic needle, 

 and therefore the changes of temperature, are registered, the marks 

 on the paper, if connected by lines, forming a curve. Unless the 

 trepidation which arises from the extreme mobility of the needle are 

 prevented, the registrations can be effected only at certain intervals 

 of time ; and in every instance the multiplier must, by means of a 

 case, be protected from currents of air. 



New Process for oetaixixg Oxygen orChloetxe. — This process, 

 which is due to M. Mallet, is founded on the properties possessed 

 by protochloride of copper (Cu 2 Cl) of absorbing oxygen from the 

 atmosphere, and becoming oxychloride (CuCl. CuO), which, when 

 heated to a temperature of 400° C, gives up the oxygen, and again 

 becomes protochloride ; the process being capable of repetition, 

 without loss, any number of times with the same protochloride. 

 The latter, to prevent igneous fusion, is mixed with some inert 

 substance, such as sand ; and on the large scale the retorts should 

 be capable of rotation, for the purpose, during the separation and 

 reabsorption of oxygen, which may be effected in the same vessel, 

 of equalizing the temperature and keeping the materials well 

 mixed. On the small scale, the process may be carried on in a 

 glass retort, from which the protochloride is removed when oxygen 

 is to be reabsorbed. Reabsorption takes place rapidly with a 

 suitable current of air, especially if the materials are slightly 

 moistened. The same materials and apparatus may be used for 

 obtaining chlorine. For this purpose hydrochloric acid is added to 

 the perchloride after it has absorbed oxygen. The gaseous chlorine 

 disengaged in soda works may be used on the large scale. Bichlo- 

 ride of copper is formed, and chlorine is obtained from this. 



Heliochromy ox Paper. — The production of pictures in their 

 natural colours has long excited the utmost interest, and will 

 continue to do so until complete success in that direction shall have 

 crowned the efforts of the photographer. What has been already 

 done, though very far from what might be wished, is enough to 

 afford well-grounded hope of the ultimate attainment of so desirable 

 an object. Progress in this department of photography is, no doubt, 



