70 



water to act as a non-conducting layer, and a covering of thick 

 felt is placed over the door for a similar purpose. A glass gauge 

 indicates the level of the water. The lower part of the water- 

 space is prolonged downwards into a pyramidal receptacle, which 

 holds a considerable quantity of water to diminish, the risk of 

 rapid changes of temperature. It is heated by two gas burners 

 with mica chimneys. 



266. Auxanometer for recording the rate of growth 

 of plants. 



E. 254. 1877. Made by E. Stohrer, Leipzig. 



A thread is attached to the growing tip of the plant and 

 carried upwards over a pulley, the edge of which is provided 

 with extremely fine teeth. A delicate spring rests against these 

 teeth and is so arranged that as each one passes it an electric 

 current is made and broken. In the same circuit is a writing 

 point which marks upon a disc of paper rotated by clock-work. 

 The result of this arrangement is that at every increment of 

 about half a millimetre (^ inch) in the height of the plant a 

 deviation from the circle is made by the writing point. 



267. Auxanometer of more modern pattern. 



Made by the Cambridge Scientific Instrument Go. 

 E. 33. 1887. 



The growing shoot of the plant is attached to a lever which 

 writes upon a revolving drum, the increment in the length of 

 the plant being highly magnified. By an attached clock-work 

 the drum can be made to rotate one tooth of a ratchet every , \, 

 or 1 hour, so that the increase in length of the plant during 

 any time can be ascertained from the tracing on the drum. 



268. Apparatus, devised by Prof. F. Cohn, Breslau, 

 for demonstrating Knight's experiment on the influence 

 of gravity on the direction of the growth of roots and 

 stems of budding plants. 



From the Institute of Vegetable Physiology, University 

 of Breslau. 



E. 253. 1877. 



The apparatus consists of a hexagonal tin box with vertical 

 sides, through the central points of which runs a horizontal 

 axle supporting a small disc of cork and a waterwheel which 

 serves to rotate it. A pipe passing through the cover of the 

 box supplies the necessary water. The mode of using is as 

 follows : 



Some seeds (by preference Pisum sativum and Zea mays) are 

 soaked for 24 hours in water, and then attached by long needles, 

 which must not pass through the radicle or the plumule, but 



