Report on Marine Meteorological Observations. 375 



of the value of the conclusions to which this investigation is likely 

 to lead, it has been considered worth while to undertake the pro- 

 digious labour of calculating the five-day means of the most reliable 

 existing observations during a century past. This work is already 

 far advanced ; and it cannot be too stronglj' recommended, that at 

 all fixed stations, where observations shall hereafter be made with 

 sufficient care to be worth recording, five-day means may invariably 

 be added to the daily, monthly, and annual means into which the 

 observations are usually collected. The five-day means should always 

 commence with January 1, for the purpose of preserving the uni- 

 formity at dift'erent stations, which is essential for comparison : in 

 leap years, the period which includes the 29 th of February will be 

 of six days. 



In treating climatology as a science, it is desirable that some 

 correct and convenient mode should be adopted, for computing and 

 expressing the comparative variability to which the temperature in 

 different parts of the globe, and in different parts of the year in the 

 same place, is subject from non-periodic causes. The probable 

 variability, computed on the same principle as the probable error of 

 each of a number of independent observations, has recently been 

 suggested as furnishing an index " of the probable dailj^ non-periodic 

 variation " at the diflferent seasons of the year ; and its use in this 

 respect has been exemplified by calculations of the "index" from 

 the five-day means of twelve years of observations at Toronto, in 

 Canada (Phil. Trans. 1853, Art. V.). An index of this description 

 is of course of absolute and general application ; supplying the 

 means of comparing the probable variability of the temperature in 

 different seasons at different places (where the same method of com- 

 putation is adopted) as well as at the same place. It is desirable that 

 this (or some preferable method if such can be devised for ob- 

 taining the same object) should be adopted by those who may desire 

 to make their observations practically useful for sanitary or agri- 

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

 climatic jieculiarities are required to be known. Having these three 

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

 resjiect 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 whicli 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 jiractical 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 



