46 



CONSERVATIOX DEPARTMENT 



Temperatures.''' — For the determination of snrface temperatures 

 an ordinary laboratory thermometer reading to 1/5 of a degree 

 Centigi-ade\vas used. For sub-surface Avork the conventional type 

 of deep-sea thermometer manufactured by the firms of Negretti 

 & Zambra and Kichter & Weise were used. The Negretti instru- 

 ments were graduated to fifths of a degree Centigrade and the 

 Richter's to tenths in the same scale. 



Transparency. — The Secchi disk, eight inches in diameter, was 

 used for determining the transparency of the Avater. The trans- 

 parency is expressed as the depth in meters at which the disk dis- 

 appeared from view. 



Currents. — Two meters were used in investigating the currents 

 of the lake. For direction the Ekman type was used. In this 

 small shot are released from a reservoir by the turning of the 

 mechanism and after passing along a grooved compass needle fall 

 into a compartmented box. For velocity the newest electric- 

 acoustic type of meter manufactured by the Gurley Company was 

 used. The results of the Ekman were not very satisfactory as the 

 mechanism showed a tendency to stick. Due to deficiencies in the 

 Shearwater's equipment she could be anchored in only the very 

 calmest Aveather and current determinations Avere consequently 

 limited to these times. 



The shape of the lake bottom in the region investigated is 

 clearly shoAvn by the bathymetrical chart, (fig. 3), Avhereon contour 

 lines are laid doAAai at 10 meter intervals. The areas of the 10 

 meter levels and their percentage of the total surface area (1701 

 sq. mi.) are as folloAvs: 



Table 3. — Ten-meter Intervals Showing Percentage of Surface Area 



Distribution of Temperature. — Although Lake Erie as a wlu^le 

 did not freeze over in the Avinter of 11)27-1928, there Avas closely 

 ])acked field ice extending AvestAvard from l>ufTalo as far as the 

 eye could reacli on May If) and for several days thereafter. 

 This ice had been in this region for sonu^ tinu^ and had come doAvn 

 there from the up|)er hike.s. It is, therefore, ])r()bal)le that on this 

 date the temperature oi' the lake as a wliole and from top to bot- 



See page 55. 



