THE ORES. 57 



ordinate scale pasted on a board was hung directly behind the group of 

 crystals, the growth of which was to be measured, and a transit instrument 

 was placed at a convenient spot at from 10 to 15 feet in front of the scale. 

 It was found convenient to use a transit, as the construction of this instru- 

 ment permitted the removal of the telescope without the derangement of 

 the tripod, and as the moisture collected so fast on the lenses within the 

 telescope that it was impossible to observe the crystals if it was left under- 

 ground over night. When the telescope was replaced it could be put 

 exactly in its former position, thus preventing any inaccuracies which might 

 arise from the removal of the point of observation from the original line of 

 sight. The temperature in this case remained at nearly 54^° F. (30.1 C), 

 the variation not being 1 J° F. during the whole time (some six weeks) over 

 which the observations extended. The moisture in the atmosphere was very 

 near the dew-point, as was shown by a very slight decrease in the tempera- 

 ture upon moistening the bulb of the thermometer. The water was drip- 

 ping from many points in the roof of the cave, and the sides were wet 

 with it. 



During the first period of observation the maximum growth of any of 

 the crystals observed was five-sixteenths of an inch in three weeks. This 

 particular crystal began its growth in a large drop of water, which gradu- 

 ally diminished in size until at the end of three weeks it had totally disap- 

 peared. During the first part of this time the crystal formed most rapidly, 

 and seemed to shoot out of the drop of watei\ Its increase was then per- 

 ceptible from day to day. The growth of this crystal, as well as others in 

 the group, was evidently dependent upon the size of the drop of water sur- 

 rounding it, for although the whole of the group of crystals was wet increase 

 was only perceptible in those crystals surrounded by a drop of water. No 

 definite growth within a given time could be fixed upon as normal. 



The maximum growth in another aggregation of crystals observed for 

 a like period of three Aveeks was found to be thi - ee-eighths of an inch, and 

 the general conditions and results were similar to those noticed in the first 

 instance. It will be noticed that the evaporation of the drops of water was 

 comparatively rapid, notwithstanding the fact that the temperature was close 

 to the dew-point. This is explained b}* the character of the ventilation of 



