12 
and by their use we have in theory a lens of three or four 
times the length of focus of an ordinary lens, and actually one 
giving the effect of sucha lens though only about one-half 
the length of focus. Being mounted in aluminium the weight 
is not an obstacle to their use. 
59. DALLMEYER MODERATE POWER TELE-PHOTOGRAPHIC * 
ATTACHMENT. This may be attached to any lens, and does 
not interfere with the ordinary working of such a lens when 
used alone. Any lens may be converted into a telephoto- 
lens by employing a negative lens of one-half the focus of the 
positive lens. 
60. COMPARATIVE PHOTOGRAPHS made with above lenses and 
with lenses of the ordinary rapid rectilinear type, showing 
the enlargement obtainable with the tele-photographic lens. 
61. THE ACTINOGRAPH. An instrument for calculating the 
exact exposure necessary for sensitive photographic plates. 
The date, time of day, lens-diaphragm used, character of the 
light and the speed of the plate are the factors employed. 
62. WATKIN’S ExPOSURE METER. An instrument for similar 
purposes, serving also for the calculation of time required for 
enlarging and printing. The actinic power of the light, 
character of subject, make of plate and diaphragm used are 
taken into account. 
63. THE ZEISS PHOTOMICROGRAPHIC APPARATUS for making 
photographs of microscopic objects. From the School of 
Mines. 
64. COLLECTION OF ALBERTYPES IN COLOR, made by Albert 
of Munich. 
65. COLLECTION OF ARTOTYPES IN COLOR, made by Edward 
Bierstadt of New York. 
66. PHOTOGRAVURES IN COLOR, made by Bussod, Valadon & 
Co.; of Panis: 
67. LICHT-DRUCK IN COLOR, made by Hanfstengel of Munich. 
Nos. 64-67 inclusive exhibited by Prof. C. F. Chandler. 
