104 



HARDWICKE'S SCIEN CE-G OSSIP. 



tion from each of the members would suffice to de- 

 fray priuting expenses, supposing the book did not 

 find a ready sale, which I think it would. 



For my own part I would do my best to aid by 

 searching the Herts localities, as Mr, Lees proposes 

 to doof Durham. Theoneobjection.I may add, is that 

 making known the localities would endanger some 

 of the plants, but I think the benefits will outweigh 

 the disadvantages. I might say a few words on 

 some of tbe rare plants of Herts. Crocus vermis 

 still grows at Mimms and Totteridge. Fritillaria 

 meleagris also at Barnet and Totteridge. Ajuga 

 cliameepitys in its old locality, at Pegsdon, near 

 Hitchin, with Iberis aniara. Bunivni bulbocastanum, 

 though less plentiful, is still abundant in one or 

 two localities near Hitchin. I am afraid that the 

 Tcry rare Orobanche cmrulea is extinct in' Herts, as 

 the place it occupied is ploughed up ; also Lycopo- 

 dium clavafvm, which grew on Tring Heath, is gone, 

 the heath being partially enclosed. Though most 

 of the boianists who compiled the records of old 

 localities are dead or aged, as Mr. Lees remarks, 

 I think we should find aid fiom such as are able to 

 give it. In conclusion I may add the motto of the 

 Herts Flora : " Turpe est in patria vivere et patriam 

 ignorare." (Linnaeus, " Fauna Suecica.") — Thomas 

 Bates Blow, Welwyn, Herts. 



SACCHARO-POLARISCOPE. 



IF "F. M. S." possessesamicroscope, hecan with 

 very little expense turn it into a polariscope 

 substituting a gulta-percha tube about a foot in 

 length, and of sufficient diameter to receive one of 



Fig. 62. Needle to denote arc of polarization. 



the eye-pieces, and allow it to revolve freely, for the 

 body of the instrument : the base of the tube must 

 be closed by a disc of the same material, in which a 

 central aperture has been made, and over which a 

 disc of glass has been cemented. Prepare a wooden 

 disc about three inches in diameter, with a central 

 aperture of the diameter of the exterior of the tube, 

 over which it should be fitted flush with the edge 

 of the tube : upon this disc should be pasted a card, 

 upon which a circle divided into degrees has been 

 drawn. A needle must be fixed on the the eye-piece, 

 in order to denote the arc of polarization : this can be 

 readily made of a piece of thin brass or even tin. The 

 above diagram will at once explain how it can 



be done. In the aperture is placed the lower portion 

 of the eye-piece ; the collar A is pushed up to the 

 milled edge of the eye-piece (the indicator should 

 fit tightly upon it to prevent any shifting when the 

 eye-piece is revolved) : over the eye-piece place a 

 cap containing a Nichol prism. 



Beneath the tube attach the polarizerj in the 

 usual way, or a bundle of glass plates may be sub- 

 stituted for the mirror. The tube should be filled 

 to about three-fourths of its length, and when 

 properly centred is fit for use ; but for accurate 

 research a thermometer and hydrometer are es- 

 sential. 



The following diagram represents a section of 

 another form of polariscope, and will be found 

 efficient and inexpensive, as most of it can be con- 

 structed of wood. A is an upright attached to a 



Fig. 63. Cheap form of Polariscope. 



firm base; B, fixed stage, with a cup-shaped apert ure 

 in the centre for the reception of the tube C. D, 

 an adjusting-arm (made to slide up and down, in 

 order to receive tubes of various lengths) support- 

 ing the tube C, and on which is fitted the analyzer 

 E, revolving on a flange attached to the arm D. E, 

 analyzer, to which is fixed the index a;b, a double- 

 image or Nichol's prism ; c, eye-lens ; d, diaphragm ; 

 e, a short tube attached to B, for the purpose of 

 carrying a Nichol's prism for polarizing, instead of 

 the bundle of glass plates E, for which an ordinary 

 silvered reflector must be substituted. The gradu- 

 ated circle may be attached to the arm D. 

 - Before placing the tube containing the liquid in 

 position, the zero must be fixed: if a doubly refracting 

 prism is employed as analyzer, this will be when 

 the ordinary image is only visible ; if a Nichol's 



