Uses of the Projection Lanterns. 157 



steam cylinder; Andrews' press; the action of capillary tubes; density-maximum of water, and 

 many others. 



The apparatus in question are placed upon a stage set up between the condenser and objective, 

 or direct on the optical bench. This does not necessitate any alterations to the lantern. A complete 

 list of apparatus suitable for projection is contained in the Price List. The audience soon gets used 

 to seeing the images appear on the screen upside down; if it is required that the pictures should appear 

 upright, a reflecting prism (Xos. 51.040 51,043) is used. 



Horizontal Projection. 



The term horizontal projection may be taken to mean the projection of transparent objects 

 placed in a horizontal position. This mode of projection is chiefly employed in connection with ex- 

 periments made in flat dishes (especially with liquids), in chemical experiments and crystallisation, 

 many of these being carried out in watch glasses; also for demonstrating the use of Berghoff's appa- 

 ratus for explaining the theory of lines of force; for demonstrating the galvanometer, etc. A special 

 Horizontal Projection Apparatus (Xos. 51,032 51,039) is required for these experiments; in this appa- 

 ratus the light pencil issuing from the condenser horizontally is directed vertically, conducted through 

 the apparatus, and subsequently redirected horizontally towards the screen. When using these appa- 

 ratus, special attention should be paid to the notices included under the various numbers, regarding 

 the removal of the front condenser lens and the entire condenser; a separate objective is unnecessary 

 *? when using the horizontal projector. 



n 



The Projection Lantern as Source of Light for Optical Experiments. 

 .3 



Many-sided are the uses of the projection lantern as a source of light for optical experiments. 



The lantern very often replaces the heliostat. which in numerous instances it is impossible to use owing 



o to the lack of sun. For such purposes the lantern is usually employed with the optical bench but without 



the objective. It seems superfluous to mention all the different optical demonstration apparatus for 



showing the propagation of light, the reflexion and refraction on plane and curved surfaces, the disse- 

 *3 ruination of colour, sensations of vision also for demonstrating optical instruments, interference, dif- 

 2 fraction, polarisation and double refraction, etc., which require a special source of light, and which 



of course show all the phenomena more plainly the stronger the source of light. We carry a large selection 



of such apparatus and in this connection we would make reference to the Optics section of our list. 

 a In the present section dealing with Projectors and accessories, we have only included these optical 

 S apparatus which are specially intended and arranged to be used with the lanterns and which cannot 



be employed with any source of light. 



Converging Light is available in connection with the lanterns in the path of rays immediately 

 behind the condenser lens. Parallel Light is produced with the aid of the bi-concave lens Xo. 50,979 

 to 50,981. The holder for this lens is inserted in the stand, after removing the table or the change frame. 

 the holder being brought near to the condenser in the converging rays, until the rays are parallel. Di- 

 verging Light is secured by using the condenser alone, but at a greater distance from the same. It is 

 better, however, to utilise the diverging light emanating from the objective after the latter has been 

 placed on the optical bench. For producing a pencil of light of smaller or greater diameter, e. g., for 

 tuning fork apparatus, etc., a diaphragmic disc Xo. 50,983 should be used, the individual diaphragms 

 of which can be changed by rotating. The disc is fixed to a haft by means of which it can be inserted 

 in the sliders of the optical bench. 



For the other experiments of an optical character it is necessary to have a corresponding number 

 of sliders having stands (Xos. 50.974 and 50.975) for setting up nicols, lenses, etc.; for all cases it will 

 be sufficient to have 5 Sliders with stands (Xo. 50,974) and i Slider with stand and being movable later- 

 ally by a screw motion (Xo. 50.975). A Avater trough (Xo. 50.976 to 50.977) is recommended for all 

 experiments if the lantern used is not fitted with a cooling chamber between the lenses of the condenser. 

 A cooling vessel is absolutely necessary for polarisation experiments and the introduction of micro- 

 scopic preparations. 



Spectrum Phenomena. Projecting a Spectrum. An adjustable Slit with micrometer screw 

 Xo. 50,986, adjusted to an aperture of about l /., mm is placed in front of the condenser. For this pur- 

 pose the Slit fitted with Iris Diaphragm (Xo. 50,988), which can be vertically or horizontally adjusted 

 at will, and which permits of varying the length of the slit, is also very good. 



