INSTRUMENTS AND TECHNIQUE 37 



Razor-blade holder — In giving a final superb finish to the wood 

 surface, nothing has been found to replace the razor-blade. Files, 

 emery cloth, and scrapers always leave the edges of the wood cells in 

 a ragged state. This may be overcome to some extent with kerosene, 

 oil, or furniture polish, but after clean cutting with a sharp razor-blade 

 the oil finish is far superior. Also, in decayed or burnt wood, after 

 treatment with paraffin, the razor leaves a surface which will permit 

 adequate magnification. Different forms of mounts could easily be 

 made, but a round steel handle split down an inch with a hack-saw 

 and a good screw to draw the split ends together serves as a very 

 convenient mount for the safety-razor blade. 



Paraffin treatment — Soft or mealy wood or charcoal is rendered 

 workable by a treatment with paraffin dissolved in gasoline or benzine. 

 This solution should be applied copiously, so that it may enter deeply 

 before it dries. Putting the whole specimen into a jar containing the 

 solution has been found very satisfactory where practicable. Boiling a 

 frail specimen in paraffin is an excellent method of preservation to 

 apply while out in the field. 



MEASURING INSTRUMENTS 

 EARLY FORMS 



Ruler — As would be expected, the first measures were made by 

 readings from a steel ruler on edge against the wood. These measures 

 were all made by the writer and were subject to the errors of estimating 

 tenths of a millimeter, but in coarse rings such errors play very little 

 part. 



Cathetometer method — This method was worked out for the very 

 long sequoia records and is still regarded as the standard method. 

 It was described in Volume I and need not be repeated here. 



PLOTTING MICROMETER 



It seemed possible to save a large amount of time by some method 

 of plotting direct from the wood and a special instrument has been 

 designed and constructed for the purpose. 



General plan — In general plan the instrument has a fairly inexpen- 

 sive screw, 6 inches long by about 1 cm. in diameter, with threads 

 having a pitch of 1 mm. A knurled head and a graduated head are 

 attached at the right end for turning and for special reading if desired, 

 but the graduations have not been used (see Plate 5) . 



The nut on this screw, by a single point of contact, moves a carriage 

 supported on a separate track. The carriage has two upright pieces, 

 between which a small telescope swings on a horizontal longitudinal 

 axis. The left end of the main screw opposite the graduated head has a 

 knurled head which is removable. Below this head, but not in contact, 



