50 



Bulletin Santa Barbara Society of Natural History. Vol. 



top and bottom. An index (A P) to show the ex- 

 pansion, I made from very thin steel rolled for steel 

 pens, by cutting with scissors, a narrow strip fifteen 

 inches long-, half an inch wide at one end and running" 

 to a sharp point at the other. This point having been 

 made as fine and sharp as possible, and a small hole 

 drilled near the other end, the index was fastened in 



place by driving a needle 

 (A) through this hole 

 into the book case, about 

 an inch to the right and 

 a little above the rod, so 

 that when the index rest- 

 ed on the top of the rod 

 it would be nearly hori- 

 zontal. Before the index 

 was put in place it was so 

 cut as to leave a sharp 

 point (D) on the the low- 

 er side to rest on the top 

 of the rod, or rather on 

 the flat surface of the 

 head of a tack driven in 

 the end of the rod. A 

 similar hard surface was 

 made for the point of con- 

 tact below. 



A small scale (S)made 

 by drawing lines one 

 hundredth of an inch 

 apart on an ivory tablet, 

 was fastened behind the 

 index, so that the point 

 rested against it. A pock- 

 et microscope held by a 

 wire in front of the point served for reading its move- 

 ments over the scale. 



As the accuracy of the observations were dependent 

 upon that of the scale, it should be stated that the lines 

 had been drawn with great care on a large graduating 



