464< Notices respecting New Books. 



which the denser portions of the object are placed still retain their 

 dark colour, the other parts are tinged, just according to the trans- 

 mission of the light. When impressions thus prepared are kept, they 

 gradually begin to fade, owing to the continued action of the iodide 

 of potassium, and hence the necessity of submitting them to a preser- 

 vative process. After numerous trials, that which seemed to answer 

 best, was merely immersing them in water for a few minutes, and 

 in some cases even allowing a stream of Water to flow gently on 

 them, so as to wash out the whole of the iodide of potassium not acted 

 on — in this way the agent which tends to decolorate the blackened 

 phosphate, seems to be removed. Several specimens of impressions 

 from dried leaves were shown, in which the diff^erent parts seemed 

 to be as nicely delineated, as in the other process, where the reverse 

 is given. Dr. Fyfe, however, stated, that though they seemed to 

 be preserved, yet he could not positively assert that they were so, 

 as they had been prepared only a few days. He also mentioned, that 

 owing to the unfavourable state of the weather, he had tried the 

 Camera Obscura only once, and though there Avas no sunshine, he 

 had succeeded in getting a very faint delineation, from which he was 

 in hopes that, in this way, a true representation may be obtained. 

 He also stated, that impressions may be got by using darkened 

 chloride paper in the same way. In this case the solution of iodide 

 must be much weaker than that for the phosphate, the chloride 

 being more easily acted on. In both cases the solution is made of 

 such strength, that when the paper is touched with it, it acts on the 

 phosphate or chloride feebly, and then, before being spread on, it 

 must be diluted with a little water, so as just to have it of such 

 strength that it does not act. A specimen of impression from chloride 

 was also shown. 



LXIX. Notices respecting New Books. 



All Elementary Treatise on the Tides. By J. W. Lubbock, Esq., 

 Treas. R.S., F.R.A.S., and F.L.S., Vice-Chancellor of the Uni- 

 versity of London. Lond. 1839, pp. 54 ; with two plates of tables 

 and a map.' 



WE find in the Preface to this work a notice of the origination, 

 in the hands of Mr. Lubbock, of the attention which the neg- 

 lected subject of the tides has of late years received from British men 

 of science, and of which our reports of the proceedings, both of the 

 Royal Society and of the British Association, nearly throughout the 

 present series of the Philosophical Magazine, have presented the main 

 i-esults, chiefly as given in the researches of Mr. Lubbock and Prof. 

 Whewell. Mr. Lubbock's first examination of the London Dock ob- 

 servations was undertaken in 1829, at the instance of the Committee 

 of the Society for the Diffusion of Useful Knowledge, with the view 

 of obtaining correct tables for predicting the time and height of high- 

 water for the British Almanac. When, however, the quantity which 

 is called the semi-menstrual inequality had been determined with suf- 

 ficient accuracy for practical purposes, the further researches in the 

 difficult problem, the solution of which had thus been essayed, could 



