abstracts: ornithology 409 



ENGINEERING. — The compressive strength of large brick piers. J. 

 G. Bragg. Bur. Stand. Tech. Paper No. iii. Pp. 39. 191 8. 



The purpose of this investigation was to determine the strength de- 

 veloped by brick piers of normal size as used in modern buildings, using 

 in their construction such materials and grades of workmanship as are 

 available in the United States. 



The variables considered in the investigation are: (i) The quality 

 of bricks employed with respect to grade and geographical location; 

 (2) the quality and kind of mortar; (3) the grade of workmanship em- 

 ployed; and (4) the bonding of courses or method of laying the bricks. 



The investigation comprises tests on 46 piers 30 in. X30 in. X 10 feet in 

 height, also 4 piers of the same cross sectional dimensions 5 feet in height. 

 The bricks used in their construction are representative of four widely 

 separated districts east of the Mississippi river and are classified ac- 

 cording to the following 3 grades: (i) Hard burned or best quality; 

 (2) medium burned or considered as common; (3) soft burned or poorest 

 product marketed. Three mortars were used in the beginning and three 

 grades of bond and workmanship were employed throughout the in- 

 vestigation. J. G. B. 



ORNlTHOIyOGY. — The migration of North American birds, V. 



The shrikes. Harry C. Obkrholser. Bird Lore 20: 286-290. 



1918. 

 The tables of migration dates for Lanius borealis show the daily 

 progress of its migration both in spring and autumn between the 

 northern and southern limits of its range, including the average earliest 

 dates of spring arrival for localities in its breeding area and the average 

 and latest dates of its occurrence in places throughout its winter range ; 

 and in autumn the average and latest dates of the last one observed in 

 its breeding area and of the first one noted in the localities in its winter 

 range. Similar data are given for Lanius ludovicianus and its subspecies, 

 the geographic distribution of each one of which is also outlined. 



H. C. O. 



ORNITHOLOGY. — The subspecies of Larus hyperboreus Gunnerus. 



Harry C. Oberholser. Auk 35: 467-474. 1918. 



No subspecies of Larus hyperboreus have hitherto been formally 



recognized, but recent investigation has resulted in the reinstatement 



of Larus barrovianus Ridgway as a readily separable race, differing 



