Progress of Invention. 393 



in the upper part of the binnacle, and is so constructed, that every 

 two minutes it lets fall a very small leaden shot. This shut, falling 

 on the moveable card of the compass, is conveyed by a channel to an 

 aperture in the card, in which is fixed a small glass tube, and pass- 

 ing through this tube, it falls into some one . of thirty-two radial 

 compartments, into which a small box, which has been placed under 

 the compass, is divided. As the box is immoveable, and the card is 

 moveable, it depends on the course the ship is following, which com- 

 partment a given shot shall fall into ; and the number of shots found 

 in a given compartment, will show the length of time during which 

 the vessel was steered in the direction corresponding to that division, 

 since each shot answers to a space of two minutes. The contrivance 

 is very ingenious, but, as at present arranged, it has certain defects : 

 it does not tell exactly the length of time during which the vessel 

 was steered in any direction : and at the end of a given period, 

 only the sum of the times during which a given course was held, 

 and not those times themselves can be ascertained. This, however, 

 is not so inconvenient as might at first be supposed. 



Simplification of the Galvanic Battery. — It has been found 

 by M. Manuelli Giacomo, that sulphate of zinc may be substituted 

 for the sulphate of copper in a Daniel's battery, without lessening the 

 power of the battery. The effects of such a substitution is a con- 

 siderable saving of expense, since the cost is merely that of the 

 zinc consumed. He found also that a very good galvanic current 

 will be produced, if zinc is substituted for the copper of the battery. 

 In this case, the zinc constitutes both the electro positive and 

 electro negative metal. 



New Application of Gelatine. — The addition of glycerine to 

 gelatine imparts to it new and valuable properties : the mixture 

 solidifies on cooling, without ceasing to be ductile. Common glue 

 mixed with one-fourth glycerine, becomes very similar in properties 

 to caoutchouc, thus it will remove pencil marks from paper : it may, 

 also be used as a varnish. 



A New Photometer. — The transparency of the air on the ap- 

 proach of rains, so that distant mountains become more distinctly 

 visible, has long been recognized as an almost certain prognostic of 

 approaching rain. This transparency is usually considered to arise 

 from the presence of watery vapour ; but is said to be partially due 

 to the rendering transparent, or precipitation of, organic matter. 

 This is inferred from the fact that U\e air coming across arid deserts 

 is transparent in dry weather, but the contrary in moist weather, when 

 it has traversed tracts in which the heat rapidly and abundantly 

 developes animal and vegetable life. In a moist atmosphere, the 

 distant mountain is seen more clearly, because the watery vapour con- 

 tained in the air either renders the germs of vegetables, etc., trans- 

 parent, or makes them so heavy that they fall to the ground. And as 

 the sanitary condition of the atmosphere is intimately connected with 

 the presence of organic matters in it, an instrument capable of mea- 

 suring the transparency of the air, and, therefore, of indirectly in- 

 dicating the amount ot organic matters which it contains, becomes 

 of some importance. M. De La Rive has recently constructed an 



