Zodiacal Light. 151 



with three of my astronomical pupils, all distinguished for 

 acuteness of vision. At 7 o'clock, Venus being near the 

 horizon and hid behind a cloud, we could severally define the 

 boundaries of the zodiacal light. By fixing the right eye on 

 the milky way near Altair, and the left eye near the head of 

 Capricornus, we could discern a pyramid less bright than the 

 milky way, but still sufficiently distinct to be sure of its 

 presence. Its upper edge grazed a and im Capricorni and ^ 

 Aquarii, its vertex reaching to the right shoulder of Aqua- 

 rius ; light very feeble and difirise, but the triangular space 

 between it and the milky way, embracing the Dolphin, per- 

 ceptibly darker ; elongation from the sun 90°." 



As a description of the zodiacal light sufficient to guide the 

 observer, I will off*er the following : From the middle of Sep- 

 tember until the latter part of November, he will confine his 

 attention to the morning sky. An hour and a half before 

 daybreak (which is at that season of the year, in our climate, 

 about 4 o'clock) he will first discern a feeble, diff"use, and 

 scarcely visible light of a pyramidal figure, extending from 

 the horizon upward through the zodiac to Gemini, covering 

 Regulus and Presepe, and terminating a little south of Castor. 

 Near the horizon its material is usually mixed up with the 

 vapours that prevail there, so as to prevent its forming a 

 definite boundary at its base ; but from an altitude of a few 

 degrees above the .horizon, the light gradually declines until 

 it fades into nonentity. Along the central part- of the pyra- 

 mid the illumination is greater than at the borders. From 

 the greater length and amplitude revealed to us by circum- 

 stances peculiarly favourable for observation, we have reason 

 to think that, on ordinary occasions, we do not see the 

 whole of the body, but that it really extends farther than its 

 visible boundaries, both in length and breadth. If the ob- 

 server continues to watch this body from the middle of Sep- 

 tember onward through the month of October to the middle 

 of November, he will perceive that the vertex or visible ter- 

 minus moves along through the order of the signs, and 

 nearly at the same rate with the sun, appearing, on the 25th 

 of October, to occupy the space south of Denebola in the tail of 

 the Lion, terminating a little above Regulus. From this time 



