444 Substitutes for an Observatory. 



the whole left until quite hard, when it may be finished off 

 with a coat of black japan. The advantage of the india- 

 rubber ring is, that it effectually prevents the possibility of 

 that most annoying accident — the running in of the varnish to 

 the cell. I have had now for several years crystals mounted 

 in this way which are quite as perfect as when first put up. 



In some cases, however, the use of a preservative fluid is im- 

 perative. Citric and tartaric acids, and carbonate of soda, for 

 example, will not keep if mounted dry. For these, castor-oil 

 — first recommended, I think, by Mr. Warington — must be 

 used, the india-rubber ring dispensed with, and the cell made 

 in the ordinary manner with cement. But, with castor-oil, 

 neither gold-size or black japan will do for making cells. They 

 must be made of sealing-wax varnish, or, better still, of " dia- 

 mond cement." The latter is, of course, used hot. JSTapthaline 

 must also be mounted in fluid, as its volatility is so great that 

 I have never been able to make a cell tight enough to keep it 

 in. Glycerine, however, answers admirably for napthaline. 

 The cell must, in this case, be made and closed with a solution 

 of ism glass in water, as the vapour of either spirit of wine, 

 naphtha, or turpentine, rapidly acts upon the delicate feathery 

 crystals. 



Where the crystallization is made upon a cover glass in- 

 stead of directly upon the slide, the thin disc must be attached 

 to the glass slip with a solution of Canada balsam in chloro- 

 form, taking care to avoid air-bubbles, and then mounted with 

 the india-rubber ring and cover glass, as described. In this 

 case no fluid can, of course, be used as a preservative which 

 has a solvent action on Canada balsam. 



SUBSTITUTES FOE AN OBSERVATORY. 



BY THE REV. N. S. HEINEKEN. 



I have been — I daresay in common with many other readers 

 of the Intellectual — greatly interested in the descriptions of 

 Observatories given by the Rev. E. L. Bcrthon and Mr. Slack 

 in your pages. To the casual observer, hoAvever, the comforts 

 of an observatory are generally things only to be hoped for. 

 I am, therefore, induced to forward to you an account of tho plan 

 which for several years I have adopted to guard against 

 draughts of air when observing in-doors. When the top sasli 

 of the window is let down, I have a square of cloth which J 

 can fix so as to fill up the whole opening. In the centre of 

 this cloth, a circular hole is made about fifteen inches in 

 diameter, in which is sewn what may be called a taper sleeve, 



