6o THE POPULAR SCIENCE MONTHLY, 



its preparations after washing ; and grease the wheels of our carriages 

 with another to make them run smoothly. Finally, we use the oil to 

 burn in our reading-lamps, and light ourselves at last to bed with 

 stearine-candles. Altogether, an amateur census of a single small 

 English cottage results in the startling discovery that it contains 

 twenty-seven distinct articles which owe their origin in one way or 

 another to the cocoa-nut palm. And yet we affect, in our black in- 

 gratitude, to despise the question of the milk in the cocoa-nut. — Corn- 

 hill Magazine, 



LOJ^GEYITY OF ASTEONOMEES. 



By Dr. A. B. M. LANCASTER. 



THE average length of human life in civilized countries is calcu- 

 lated to be about thirty-three years. This mean apf)lies to the 

 whole of the population of a country. But certain distinctions may 

 be made, between different professions for example, among which con- 

 siderable variations are observable. It is easy to believe that some 

 professions would have the general effect of increasing the probable 

 duration of life, while others would abridge it. It is generally ad- 

 mitted that men devoted to scientific pursuits enjoy the expectation 

 of a considerably longer life than the average. We have been curious 

 enough to inquire how much foundation for this opinion there is in 

 the case of astronomers, whose observations, calculations, and studies 

 imperiously require a quiet, sedentary, and regular life. Our investi- 

 gation has been facilitated by MM. Houzeau and Lancaster's " Biblio- 

 graphic Generale de 1' Astronomic," in the biographical chapter of which 

 we found all the information we needed. In this chapter are given 

 the date of birth and death of 1,741 astronomers, of periods reaching 

 from the most ancient times to our own days. Calculating the mean 

 length of life of the whole 1,741, we have found it to be sixty-four 

 years and three months. Fully to appreciate the value of this figure, 

 we must compare it with that representing the average expectation 

 of life at the age at which the astronomer may be supposed to have 

 begun his career. If we fix this age at eighteen years, the person 

 enjoys an average expectation, according to the mortality-tables, of 

 living to sixty-one years. The astronomer, then, enjoys an advan- 

 tage equivalent to an additional expectation of three years and three 

 months. If we examine the ages to which they actually lived, we find 

 that, out of a thousand astronomers, 596 lived to be seventy years old ; 

 260 to between seventy and seventy-nine ; 126 to between eighty and 

 eighty-nine ; 15 to between ninety and ninety-nine ; and three to be 

 over a hundred years old. 



Taking a population in mass, say that of Belgium, of a thousand 



