MICROSCOPICAL TECHNIQUE. 73 



It seems that we have still a good deal to learn with respect to 

 this matter. Perhaps we may liken the periodicity of the sun to 

 the periodicity of the great geysers in Iceland. In the latter phe- 

 nomenon there is a sudden outbreak of heated water, which occurs 

 with some regularity in a certain number of hours after the last 

 outbreak. There is a somewhat similar pulse in the sun, and, 

 considering the fire of the body involved, it is not surprising that a 

 period of eleven years should divide two successive outbreaks. 

 But how it is that these solar phenomena should be able to set our 

 magnetic needles into a tremble is a matter to which science has 

 not as yet been able to give a quite satisfactory answer." 



— The Standard^ Oct. 20, 1892. 



flDicro6copical ^ccbniquc. 



Compiled by W. H. B. 



Glycerine- Mounting.^— Mr. C. E. McClung writes on the merits 

 of glycerine as a mounting medium. He finds the advantages of 

 glycerine are its being non-volatile, colourless, slightly affected 

 by changes of temperature, has a high refractive index, and remains 

 perfectly colourless for any length of time. " The glycerine should 

 be pure and free from dust and air-bubbles. To keep it free from 

 these contaminations, devices such as are recommended by Car- 

 penter and Prof. James are excellent. These are bottles containing 

 the glycerine and provided with glass tubes, whereby the glycerine 

 IS forced out by air-pressure. The cements may be of a balsamic 

 nature, but preferably zinc oxide or asphalt. Any cement not 

 aftected by the medium may be employed, but experience has 

 proven that the two above named are the best. The other essen- 

 tial parts of the completed mount are the slip and cover-glass. 

 No special mention is made concerning these except that they 

 should h^ perfectly clean. To ensure this, the practice of leaving them 

 until ready for use in a bath of ordinary battery fluid is recommend- 

 ed. Upon the consistency of the cement depends, in a great mea- 

 sure, the formation of a good cell. It should not be thin enough 



* The Microscope, xii. (1892), pp. 201—203. 



