102 PEOFESSOE BUTSCHLIS 



drops creep to and fro in water, or in half-diluted glycerine, 

 even when they are not compressed. The streaming movement, 

 on the other hand, is better seen if the drops are somewhat 

 compressed, which may be done by inserting under the cover- 

 glass a piece of a broken cover-glass of medium thickness, and 

 then removing the paraffine pegs. Then draw away the liquid 

 until the necessary pressure is obtained. This streaming 

 movement is best demonstrated twenty -four hours after the 

 addition of the glycerine^ as the drops will then be thoroughly 

 cleared and transparent. Further, it is interesting to note 

 that a progression of the drops takes place in the direction in 

 which the streaming moves. 



As this forward movement is rather slow in compressed 

 drops, it is necessary to use a micrometer ocular to satisfy one- 

 self of the advance. 



Unfortunately the oils which I have prepared since my first 

 experiments do not move and stream so well or so rapidly as 

 those I employed then. The movement and streaming show 

 themselves much more markedly and distinctly if they are 

 examined on a warmed stage at a temperature of 50° C. If 

 you should be in a position at your demonstrations to conduct 

 the experiment at this temperature, the phenomena will cer- 

 tainly be much more evident. 



From the preceding description you will see that it will 

 be necessary, to obtain good results, to gradually get hold of 

 the methods, and you must not doubt the correctness of the 

 phenomena which I have described if the first trials do not 

 give the desired results. 



At all events, you will have at first to make some experi- 

 ments so as to obtain an insight into the conditions and sort 

 of phenomena, but I do not doubt that you will succeed iu 

 observing the appearances and in demonstrating them to others, 

 though perhaps in not so vigorous a degree as I might 

 desire. 



I have lately made some trials to render olive oil 

 suitable for these experiments by heating it more rapidly. 

 Although at present I have no entirely reliable results, it 



