610 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fig. 119. 



To this category belong, for instance, the supposed oscillations of the 

 OscillariecB, whose changes of level, when thus in motion, were 

 formerly unnoticed. 



In addition to these characteristics of a spiral motion it must, of 

 course, be ascertained whether it is right- or left-handed. To dis- 

 tinguish this in spherical or cylindrical bodies which revolve round a 

 central axis is by no means easy, and in many cases, if the object is 

 very small and the contents homogeneous, it is quite impossible. The 

 slight variations from cylindrical or spherical form, as they occur in 

 each cell, are therefore just sufficient to admit of our perceiving 

 whether any rotation does take place. The discovery of the direction 

 of the rotation is only possible when fixed points, whose position to 

 the axis of the spiral is known, can be followed in their motion round 

 the axis. The same holds good also, mutatis mutandis, of spirally 

 wound threads, spiral vessels, &c. ; we must be able to distinguish 

 clearly which are the sides of the windings turned towards or turned 

 away from us. 



If the course of the windings is very irregular, as in fig. 119, a 

 little practice and care is needed to distinguish a spiral line, as such, 

 in small objects. The microscopical image might easily 

 lead us to the conclusion that we were examining a 

 cylindrical body composed of bells or funnels inserted 

 one in another. The spirally thickened threads, for 

 instance, as they originate from the epidermis cells of 

 many seeds, were thus interpreted, although here and 

 there by the side of the irregular spirals, quite regular 

 ones ai-e also observed. 



Moreover, it must not be forgotten that in the micro- 

 scopical image a spiral line always appears wound in the 

 same manner as when seen with the naked eye, while in 

 a mirror (the inversion being only a half one) a right- 

 handed screw is obviously represented as left-handed, 

 and conversely. If, therefore, the microscopical image is 

 observed in a mirror, as in drawing with the Sommerring 

 mirror, or if the image-forming pencils are anywhere 

 turned aside by a single reflection, a similar inversion 

 takes place from right-handed to left-handed, and this inversion is 

 again cancelled by a second reflection, as in Oberhauser's camera 

 lucida, and in many multocular Microscopes. All this is, of course, 

 well known, and to the practised observer self-evident ; nevertheless, 

 many microscopists have shown that they are still entirely in the 

 dark about matters of this kind." 



Brownian or Pedetic Motion* — The skipping motion of extremely 

 small particles has been for long a subject of curiosity, but in the 

 view of Prof. Ramsay has as yet remained without explanation. The 

 following is an attempt on his part to ascertain its cause. 



1. It is not dependent on the life of the particle. This would 



* Pioc. Bristol Naturalists' Soc., iii. (1882) pp. 299-302. 



