FOREIGN INTELLIGENCE. 



305 



20 to 40 fathoms depth ; both these conditions vary with the seasons and 

 the weather. 



In the chapter on optical conditions, the author states the distinction 

 between the specific coloration of sea-water and the tints due to re- 

 flection of surrounding objects ; the dependence of the specific coloration 

 on depth, purity, and transparency of the water (as proved by a great 

 number of measurements) ; and the intensity and tints of light as it pene- 

 trates into greater or less depths. When discussing the undulatory move- 

 ments, the author pays special attention to the nature and intensity of 

 breakers, as determined by the conformation of the sea-bottom and of the 

 shores ; as also to currents, their velocities and depths, and their de- 

 pendence on the direction and intensity of winds or on unequal distribu- 

 tion of atmospheric pressure and of evaporation. 



Level-observations, continued during a series of years and occasionally 

 far southward along the Dalmatian coast, have led our author to a number 

 of very peculiar, and indeed unexpected results concerning the tides of 

 the Quarnero. Within the eastern longitudinal half of the Adriatic, high 

 water and low water take place only once in twenty-four hours, their times 

 of beginning not retrograding daily with the culmination of the moon, 

 but retarded only two hours in every month, so that within twelve months 

 the tides return again to their original periods. The facts being at com- 

 plete variance with those hitherto admitted, Dr. Lorenz thought proper to 

 give a graphical representation of a long series of his personal observa- 

 tions by means of curves, which he calls " actiographical," as being indicative 

 of the causes acting on tides. The average sea-level is chosen for a line of 

 abscissa : the curves rising above or sinking below the line mark the epoch 

 and intensity of tides ; their tracing (thick, thin, punctated, streaked, etc.) 

 is indicative of the simultaneous state of weather and wind. Every diur- 

 nal curve bears the date of the corresponding day and lunar phases, and 

 is partly accompanied by the corresponding barometrical curve. This syn- 

 optical representation of tides and causes acting on them, shows that 

 none of the above-named factors, nor interferences, friction, and other 

 causes of retardation, are the ultimate causes of this peculiar march of these 

 tides, although they may modify it within precise limits. The ultimate cause 

 may only be ascertained by tidal observations extended through the whole 

 length of the Adriatic and the Mediterranean ; the phenomenon itself is a 

 duly-stated fact, and Dr. Lorenz has made it the basis of a tide-calendar 

 for the Quarnero, with every connection for secondary influences acting on 

 the times of beginning and the intensity of tides. 



The physical part of Dr. Lorenz's book ends with the discussion of tem- 

 perature as influenced in many ways by all the other factors. Nearly 200 

 measurements have been taken, either at regular periods, in determinate 

 places, and in constant depths (surface, 10, 20, and 40 fathoms), or occa- 

 sionally to serve for special purposes. The results of these observations 

 are highly interesting. They give, not only the average temperature of 

 water in the above-mentioned horizons, but also the progress of tempera- 

 ture within them during the course of each season. Their graphic re- 

 production by means of curves distinctly exhibits the retarded influence of 

 seasons, the diminution of difference between the maxima and minima, 

 and the general depression of average temperature with increasing depth 

 (about 1° R. for each 10 fathoms). The influence of the sea-bottom, of 

 fresh water, etc., on the temperature of shallows, is brought under discus- 

 sion ; and the affluent fresh waters are shown, by observations of tempe- 

 rature, to form a very thin but far-spread stratum on the surface of the 

 heavier salt-water. 



VOL. YI. 2 R 



