OF PERIODICAL NATTOAL PHEXOMEJTA. 35 



for these periodical phenomena, both of plants and animals, are all 

 more or less regulated by the laws of climate and the varying 

 influences of the seasons. It is here that union is requii-ed, for it 

 is only by the combination of the records of many observers scattered 

 over a wide area that results of importance can be obtained. That 

 the Naturalists' Calendar for the County of Hertford, which I 

 hope in time will be compiled from the observations of the members 

 of our Society, may be of value in this respect, the list of the 

 Meteorological Society is adhered to. This list is founded upon 

 the more extensive list of Quetelet adopted by Continental observers, 

 and any species it may in time be deemed advisable to add to our 

 list should be selected from this, for by so doing the results we 

 may obtain can be compared with the results arrived at on the 

 Continent of Europe and in other countries. As an example of 

 the information that may be derived from these calendars, it may 

 be mentioned that by comparing the various records of similar 

 observations, made simultaneously upon the species selected at a 

 number of stations in this and other countries, we may distinguish 

 those localities at which the same phenomena occur at the same 

 time, and by drawing lines through these localities we may indicate 

 with clearness the isochronism of the phenomena, and therefore of 

 the climatal conditions upon which they are dependent. 



It is, however, only by observations extending over a number of 

 years that the mean date of these occurrences for any locality can 

 be determined.* This is what is requii'ed. The average range of 

 variation is about a month, and it has been found to be greater with 

 the phenomena that occur early in the year than with such as occur 

 later. The long and severe winter we have had this year will 

 therefore make the earlier and later phenomena occur nearer to- 

 gether than they usually do, and we may expect the summer to be 

 not nearly so backward as the spring now is, while the autumnal 

 phenomena may not even be appreciably affected. 



It may be many years before the mean date of each phenomenon 

 for Watford and elsewhere in our county can be determined with 

 any degree of accuracy. Let us then at once commence to record 

 our observations on the species selected, and not be deterred by the 

 thought that it may not be in oiu- time that inferences of high 

 scientific value may be drawn from them. Moreover, without 

 considering the ulterior object we have in view, every accui'ate 

 obseiwation, carefully and faithfully recorded, is at once of value, 

 and available for comparison with others. The cultivation of habits 

 of observing is also in many ways beneficial to ourselves. The 

 more we observe, the more we find to observe, and the more we are 

 capable of observing ; — our senses are sharpened and we see and 

 hear things which, had we not cultivated this habit, would never 

 have been noticed. As Edward Forbes has remarked, " It is sur- 

 prising how little we see until we are taught to observe." 



* The true mean is not the mean of the extremes, but the mean of all the dates, 

 found by adding them together and dividing by their number. 



