1847.] SMITH ON DEPRESSION OF LAND. 235 



member of the base of the columns, which is about 14 inches below 

 that observed by me seventeen years afterwards. 



Professor Forbes again visited the temple in 1843, when he noticed 

 the height at which the surface stood at the base of the columns ; and 

 as I also measured the depth at the same spot, I find that our mea- 

 sures agree as nearly as possible. He says, that when they were 

 taken " the level was lower than usual, being very calm, yet the water 

 rose above the first roll of the pillar" (the Tortjs), i. e. about 20 

 inches above the floor. He adds, " there appears to be much more 

 water than when I saw it in 1826." 



He does not mention the state of the tide, but his observation must 

 have been made within half an hour of high water, as the date was 

 9th Dec. 1843, and the hour between 10 and 11 a.m. ; but it was 

 high water in the Bay of Naples upon that day about eleven, being 

 two days after full moon ; the time of high water at Naples being 

 9^ 23'° at full and change*. 



In order to enable future observers to estimate the annual rate of 

 depression vdth more accuracy than I have been able to do, I have to 

 mention that when I made my measurements there was no disturbing 

 cause to afPect the mean level of the sea in the Bay of Naples. 



The winds for some time previously had been light and variable, 

 and at the time in question (11th May, 1845, at 7 a.m.) it was so 

 calm that the oscillations of the surface did not exceed 2 inches on 

 the pier of Pozzuoli. The observations were taken exactly at low 

 water, for when engaged in examining the tunnel by which the water 

 within the building communicates with the sea, I noticed the first of 

 the flood entering it ; at that time the water stood 1^ inch above the 

 square plinth, or lowest member of the base of the southernmost of the 

 three pillars, and 9^ inches above the step upon which they rest : 

 hence it must have stood 1 1 or 12 inches above the plinth at high 

 water. 



I think it right to state that my conclusions, respecting the annual 



* As the state of the tide is an essential element in all calculations respecting 

 the rate of change of level, it is necessary that it should be stated, or at least that 

 the date and hour of the day be given, to furnish the means of making the necessary 

 correction of the observed depths. The establishment of the Port of Naples, as 

 given by Signor Nobile in the * Rendiconti dell'Academia delle Scienze di Napoli,' 

 is as follows : — High water at full and change of the moon 9 hours 23 minutes ; 

 rise and fall of the tide 378 millimetres (14-8 inches). Within the temple of Serapis 

 the rise and fall is certainly not so much ; I found the marks of the preceding 

 tide 10 inches above low water ; Cav. Nicollini states it to be nine-tenths of a 

 (Neapolitan) palm or 9i inches ; he also notices that the time of the turn of the 

 tide is well-marked (ben distinto) in the outlet ; I can confirm this by my own 

 observation. 



The meati level of the Mediterranean is of course affected by the winds. In 

 looking over Cav. Nicollini's observations, I find that the difference between any 

 two consecutive tides rarely amounts to 100 millimetres or 4 inches ; and only upon 

 one occasion is it so much as 131 or 5*17 inches; it appears, however, that he 

 omitted to record unusual elevations caused by the "buttature" or swell on the 

 outside. 



From the open form of the Bay of Naples, the sea-level must soon recover its 

 equilibrium, hence observations made in calm weather cannot be much affected by 

 this disturbing cause. 



