IX. EDUCATIONAL. 373 



1898. Ring Sphere. Dr. H. Locker mann, Hamburg. 



This armillary sphere, of which a more detailed explanation accompanies 

 the instrument, is to be used for instruction in mathematical geography. It 

 is to serve for object lessons, and makes therefore no pretence to scientific 

 accuracy. The instrument demonstrates the apparent motion of the sun and 

 moon, and of the more important constellations (49 constellations with 359 

 stars of from first to fifth magnitude) at any given place and at any given 

 time. 



1899. Projection Apparatus. T. and A. Molteni, Paris. 



1900. Sigr. Descrivani's Orrery, by M. Pierret. 



Conservatoire dcs Arts ct Metiers, Paris. 



1901. Wall Maps (11) for teaching Cosmography : 



1. The Ptolemaic system. 



2. Tycho Brake's system. 



3. The Copernican system. 



4. Comparative sizes of the sun and earth. 



5. Comparative sizes of the planets (with map of Mars). 



6. The seasons. 



7. The phases of the moon. 



8. Eclipses. 



9. Parallax. 



10. Comets. 



11. Nebulas. Ernest Recordon, Geneva. 



1902. Three Astronomical Diagrams and Two Rules, 



with scales, for the solution of problems in spherical trigonometry. 



Michael Elbe, Ellwangen. 



The graphic representations drawn on the maps are called astronomical webs 

 (diagrams), and the rules contain scales. By the assistance of a diagram 

 and a scale any problem in spherical trigonometry can be solved without 

 working out, a great advantage in navigation. It serves also' on land for the 

 determination of time and azimuth by means of one observation of a star. 



In order to obtain the necessary accuracy in navigation, the drawing must 

 be made as exact as possible by a machine, so that the accuracy of the solu- 

 tion, so far as that depends on the accuracy of the observing instrument, will 

 be fully attained. Far greater precision will be arrived at by repetition, 

 namely, by the easy reading of dozens of results which depend upon just so 

 many observations. Even the most extensive table for nautical calculation 

 cannot effect this ; besides which the inverse problem, often so difficult of 

 solution, becomes a pastime by means of this apparatus. 



1903. Chart of the Stars, southern evening winter sky, in 

 Central Europe. 



Prof. J. J. Oppel, and Dr. K. Oppel, Frankf or t-on- Maine. 



1904. Specimens of Astronomical Diagrams, for teaching. 

 White figures on black ground. J. J. OppeL 



In both instruments the circular plate (white on one side and black on the 

 other) represents the plane of illumination, at a at the time of the equinoxes. 

 The arrangement demonstrates as a necessary effect of a secular revolution to 

 the right of the plane of inclination of the earth's axis ; A the increase of the 



