MAGNIFYING POWER OF SHORT SPACES. 15 



to admit as large an angle as the lenses of the eye are capable 

 of refracting, at the same time that the object is rendered 

 distinctly visible, then, under such circumstances, we have 

 arrived at the utmost limit to the available magnifying power 

 of the eye. These conditions are fulfilled in the diascope ; 

 which may be defined to be an instrument which enables us to 

 develop the microscopic power of the eye hy retaining an object 

 close in front of it at one end, loliile it is examined by the light 

 admitted through small apertures at the other* 



With such a simple optical instrument, altogether destitute 

 of glass, a series of images may be presented which have never 

 before been seen with the naked eye ; and by its use we are 

 led to a legitimate conclusion, capable of direct proof, that 

 when a transparent figui'e is held very near to the eye for the 

 purpose of magnifying it, if an image is seen at all, its size 

 will bear an inverse ratio to the intensity of light by which it 

 is made visible. 



In my next communication, which will embody the second 

 part of the subject, I shall beg permission to describe and de- 

 lineate another set of forms distinct from those which have 

 been noticed in this, and which are produced by substituting 

 straight or circular very narrow apertures of light for the per- 

 forations. With such apertures, figures are seen as in perspec- 

 tive, lines appear expanded into planes, and these are multi- 

 plied into solids, which, from being of an ethereal brightness, 

 bear a resemblance to models of regular geometric solids of 

 pure glass. 



On the Spiral Threads of the GenusTRicuiA.. By Frederick 

 CuRREY, Esq., M.A. 



If anything were wanting to sliow the extent of the field of 

 research, which is open not only to the student but even to the 

 more advanced inquirer in botanical microscopy, it would be 

 sufficient to direct attention to some of the many points in 

 vegetable anatomy upon which the opinions of observers not 

 only differ from one another, but are so utterly and diametri- 

 cally at variance, that if the one side be right the other must 

 be altogether wrong. Commencing upon the threshold of 

 vegetable life, opinions are still divided as to the structure of 

 the primary membiane of the walls of young cells, Mulder 

 and Hasting contending that the young cell-membrane is 

 pierced like a sieve, whilst Von Mohl asserts that it is com- 



* This instrument may be procured at Mr. Highley's Scientific Library, 

 32, Fleet-street, London. 



