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Prof. Karl Pearson. 



(A). — On a Monthly Period in the Birth-rate. 



2. While it is well known that there is an annual period in the birth- 

 rate, no attempt, as far as I am aware, has been made to ascertain 

 whether a lunar period exists. Accordingly, I applied to Dr. E. C. 

 Perry, superintendent of Guy's Hospital, who most kindly placed at 

 my disposal the maternity records of that charity. As preparatory 

 work Mr. Yule and I extracted upwards of 6,000 births with their 

 dates. These, with the assistance of Mr. L. Bramley-Moore, we 

 arranged in four groups, male and female, and in twenty-nine and 

 thirty day lunar months as given by the almanack of the year. In 

 each lunar month the number of births on each successive day following 

 the new moon was tabulated, and each month was then reduced to the 

 same total, so that no month might be weighted by its relation to the 

 annual variation in birth-rate. Thus four curves were obtained, each 

 embracing the material for twenty-four months, and giving the daily 

 fluctuation in male and female birth-rate for twenty-nine and thirty 

 day lunar months. In none of these curves was there any significant 

 deviation from the diurnal average on any day. The curves were then 

 harmonically analysed by Mr. Yule ; the result gave no approach to 

 agreement between the amplitudes or phases in the four cases. Had 

 there been any approach we should have gone on to 20,000 births as we 

 originally proposed, but it seemed merely a waste of labour. I con- 

 clude, therefore, that if there be any monthly period in the birth-rate, 

 it is of very small importance. There is little or no correlation 

 between lunar phase and birth frequency. The object of this inquiry 

 was the following : The average regular recurrence of the monthly 

 period in woman has been taken to suggest a tidal influence on the 

 primitive ancestry of mankind there is an indisputable correlation 

 between birth and the date at which a monthly period would have 

 taken place had pregnancy not intervened. Hence a positive result 

 might have confirmed this suggestion of tidal influence, as well as 

 explained a certain amount of folklore connecting birth and lunar 

 influence. 



Our negative result merely shows that if lunar or tidal influence 

 ever fixed the period of the menses, sensible correlation between the 

 two has now disappeared. 



(B). — On the Correlation between Weight and Length of Infants at Birth. 



3. A table of the length and weight of infants at birth was given in 

 a " Report of the Anthropometic Committee of the British Association " 



* "In the lunar or weekly recuri'ent periods of some of our functions -we appa- 

 rently still retain traces of our primordial birthplace, a shore washed by the tides," 

 Charles Darwin, ' The Descent of Man,' p. 161, 2nd ed. 



