354 



to make their observations practically useful for sanitary or agri- 

 cultural purposes, or for any of the great variety of objects for which 

 climatic peculiarities are required to be known. Having these three 

 data, viz. the mean annual temperature, its periodical changes in 

 respect to days, months, and seasons, and the measure of its 

 liability to non-periodic (or what would commonly be called, irre- 

 gular) variations, we may consider that we possess as complete a 

 representation of the climate of any particular place (so far as 

 temperature is concerned), as the present state of our knowledge 

 permits. 



It is obvious that much of what has been said under this article 

 is more applicable to land than to sea observations ; but the letter 

 of the Board of Trade, to which this is a reply, requests that both 

 should be contemplated. 



Temperature of the Sea, and Investigations regarding Currents. 



It is unnecessary to dwell on the practical importance to navigation 

 of a correct knowledge of the currents of the ocean ; their direction, 

 extent, velocity, and the temperature of the surface water relatively 

 to the ordinary ocean temperature in the same latitude ; together 

 with the variations in all these respects which currents experience 

 in different parts of the year, and in different parts of their course. 

 As the information on these points, which may be expected to follow 

 from the measures adopted by the Board of Trade, must necessarily 

 depend in great degree on the intelligence, as well as the interest 

 taken in them by the observers, it is desirable that the instructions 

 to be supplied with the meteorological instruments should contain a 

 brief summary of what is already known in regard to the principal 

 oceanic currents ; accompanied by charts on which their supposed 

 limits in different seasons, and the variations in those limits which 

 may have been observed in particular years, may be indicated, with 

 notices of the particularities of the temperature of the surface-water 

 by which the presence of the current may be recognised. Forms 

 will also be required for use in such localities, in which the surface 

 temperatures may be recorded at hourly or half-hourly intervals, 

 with the corresponding geographical positions of the ship, as they 

 may be best inferred from observation and reckoning. For such 

 localities also it will be necessary that the tables, into which the 



