482 Life and Letters of Francis Galton 



Letter to Michael Foster, with a memoir entitled: 

 "Decrease of Mortality by Smallpox, 1838-1887." 



42, Rutland Gate, S.W. March 19, 1890. 



Dear Foster, I have gone through the paper, corrected and added. 1 am ashamed of 

 having sent it in so slovenly a way. Look at the addition to the bottom of p. 9. As the previous 

 part stands by itself it might lead to a misapprehension. I have confiscated the lithographed 

 map (of which doubtless you have plenty of copies) by marking it and attaching it to the paper. 

 It is wanted to explain. If you should find it desirable to put the paper as it now stands into 

 the evidence, I have no objection. Very sincerely yours, Francis Galton. 



The paper to which this letter refers deals with vaccination statistics. 

 The data are divided into three periods: (i) 1838-1853, vaccination op- 

 tional; (ii) 1854-1871, vaccination obligatory, but not efficiently enforced ; 

 (iii) 1872-1887, vaccination obligatory, but more efficiently enforced by 

 the vaccination officers. The treatment of the data is rendered difficult 

 by (a) the absence of records for 1843-1846 inclusive, (b) by very severe 

 epidemics in 1838 and 1871, and by lesser epidemics in intervening years, 

 i.e. the graph of the mortality rate is very jagged. Galton deals only with 

 crude death rates, he had no incidence rates. He could not therefore test the 

 effects of (i) any change in the age distribution of the population, (ii) how 

 far the lower mortality rate was due to better nursing, nor did he (iii) en- 

 deavour to allow for any hygienic improvement. The statistical methods he 

 adopts are quite simple, but adequate for his purpose, and his final conclusion 

 is stated in guarded terms : " For the whole period under review the maximum 

 reasonable decrease in the mortality rate is 500 per million and the minimum 

 reasonable decrease is 150 per million." He makes no statement as to what 

 the source or sources of this reduction may be. A discussion of the data 

 brought up to date on Galton's lines would be of interest. I am unaware if 

 the memoir was ever presented to the Royal Commission on Vaccination 

 (1889-1890), or printed elsewhere. Together with the letters of Galton, it was 

 apparently sold by the executors of Sir Michael Foster, and was purchased 

 by me from a Cambridge bookseller on May 9, 1914. This was the first 

 occasion on which I had information that Galton had ever dealt with the 

 statistics of smallpox. He never referred to that topic in conversation 

 with me, although several memoirs dealing with smallpox were issued in 

 Biometrika. 



The Philosophy of Snoring. Notes found in Francis Galton's 



Handwriting. 



The philosophy of snoring. Married ladies have remarked that husbands past the age of 50 

 or GO are apt to snore. I have enough reason to believe in the correctness of this generalisation 

 to assume it to be true and more generally to ask the reason of it. What is the cause of snoring? 

 I have not found this interesting and domestically important topic treated anywhere in a 

 scientific manner. I write for information. I have only a few ideas and observations of my 

 own of the scantiest, and mention them merely to elicit those of others. First I have been 

 surprised at the silent sleep of men in bivouac. The breathing of some 30 or 40 men, mostly 

 savages, though old men, of whom I had many months' experience in travel, was inaudible. 

 Conversely hot bedrooms stimulate snoring. Again a deep sleep is more accompanied by 

 snoring than a light one. The uvula droops more. It is analogous to the fallen jaw of death. 



