2]i> AMERICAN FORESTRY 



hollows and plate holders. In the apparatus here used, which is a Bausch & 

 Loinb "Ualopticou"' and Zeiss microsco{e, the parts are mounted horizontally 

 iu the order mentioned. The heavy iron bases supporting the several parts 

 are placed on rubber cushions under the feet as a precaution against vibra- 

 tions, as a very minute vibration of the microscope is greatly magnified upon 

 tlie screen. Non-halation orthochromatic plates have been found to give the 

 best results, although ordinary plates may be used with fair success. The 

 process of taking the photographs through the microscope does not differ 

 materially from that of taking an ordinary picture with a camera by use of a 

 color screen or ray filter. The art of making these micrographs consists 

 largely in obtaining a uniform illumination of the field and the proper focus. 

 To focus properly requires experience, as it is not possible to show on the 

 screen exactly what one sees through the microscope with the eye, since in 

 the latter case a slight adjustment is made by the eye, whereas in the camera 

 the focus is dead and in one plane only. The effect of perspective is lost in the 

 camera. Of coui-se the result in every case is absolutely dependent upon the 

 slide, which, for the best results, must be of the proper thinness, correctly and 

 uniformly stained, absolutely flat, clean and free from air bubbles. It must 

 also be of sufficient size to cover the field desired. 



To illustrate the wood structure, two or more magnifications will be used, 

 a low power of perhaps 30 or 50 diameters to show the general appearance, 

 and a higher power of perhaps 300 diameters to show the minute structure in 

 detail. Higher magnifications also will be used when it is desired to show re- 

 markable features such as bordered pits, for instance. 



The largest views taken will be eight by ten inches, which can be subse- 

 quently reduced to any size for publication. The accompanying photographs 

 are given as illustrations of the views to be shown, and are made from sec- 

 tions of Bull Pine (Pinus ponderosa). Figures 1 to 3 are magnified thirty 

 times; 4 to 6, three hundred times; and 7 and 8, eight hundred times. Similar 

 views to these are to be made of the various important species so far as any 

 visible distinctions can be shown, and an attempt made to show, as far as 

 possible, the interpretation of these features or distinctions in the outward 

 properties, and distinctions in properties, of the various woods In some in- 

 stances it is contemplated to show in addition to the sections the individual 

 separated elements. 



The work is being done by the section of timber physics, and is in the 

 hands of experts in this line. Miss Eloise Gerry, who is making the sections 

 and slides, comes to us from Dr. Jeffrey of Harvard, and Mr. Simon Kirsch, 

 who is making the photomicrographs and has general oversight of the work, 

 is from the late Dr. Penhallow of McGill University. 



It is not our belief that a study of this kind will ever fully explain the 

 differences in the mechanical and physical properties of different woods, nor 

 can it be honied to offer a means of predicting with completeness how a new 

 or unknown wood will behave. Such points must be determined chiefly, as 

 heretofore, by direct actual tests of the properties in question. Even were 

 this ])rediction jtossible, it is very doubtful whetlier it would serve any prac- 

 tical use, since ordinarily it w'ould be easier and simpler to make the direct 

 test than to cut, prepare and examine the sections under the microscope. How^- 

 ever, while it may never be possible to completely predict the properties, cer- 

 tain uses and behavior of the species under given conditions will most likely 

 be indicated and suggested and much clarity and light will be thrown on the 

 causes of the behavior of the various woods under certain conditions and 

 treatments. It has been the experience of the past that wherever knowledge 

 of fundamental truths has been brought to light, important results have fol- 



