240 MR. T. HEELIS ON THE TEMPERATURE 



second series of observations, which were taken by the 

 writer with the same, or if possible, greater care than 

 those taken on the run out. 



On the run home, in passing the mouth of the Tagus, 

 the ship was further in the offing than in the run out. 

 Hence it might reasonably have been expected, as only 

 twelve days had elapsed since the former observation, that 

 the temperature of the water would have been higher. It 

 is, however, shown to be lower, the temperatures of the 

 air being 6i*ii to 65'35, and those of the water being 

 6o"i25 to 62*525. The differences of temperature in 

 the two sets of observations are very striking, and show 

 how impossible it is to arrive at any accurate determina- 

 tions without long continued observations. 



A few words as to the mode in which the observations 

 were made may be desirable. 



On the assumption that the vessel would not exceed a 

 speed of ten knots an hour, which under steam and sail 

 was considered good speed for the "Crimean," it was 

 decided to take the observations as far as possible every 

 three hours, which would give one to each half degree ; 

 but the observations were not continued during the whole 

 night, as no practical experience in reading thermometers 

 was possessed by the officers of the ship. The thermo- 

 meter was generally hung to the belaying pins, and under 

 the lee of the mainmast, for the purpose of obtaining the 

 temperature of the air. For the water it was sometimes 

 towed over the tafiPrail, and at other times immersed in a 

 bucket of sea water drawn for the purpose. T found no 

 difference in the readings obtained by these two methods. 

 The barometer readings were taken from an aneroid which 

 was carefully compared before and after the series with a 

 standard barometer. 



The following are the observations : 



