Final Answer:
According to McBurney and Collings, the average threshold for human vision is a candle flame seen from 30 mile(s) on a dark, clear night.
a) 30 miles
Step-by-step explanation:
Human vision is remarkable in its ability to perceive light under varying conditions. According to McBurney and Collings, the average threshold for human vision is a candle flame seen from 30 miles on a dark, clear night. This means that under optimal conditions, the human eye can detect the faint illumination of a single candle flame from a distance of 30 miles.
The concept of the average threshold for human vision is based on the ability to perceive low levels of light in the dark. McBurney and Collings likely conducted experiments or studies to determine the point at which a candle flame becomes just perceptible to the average human eye. This threshold is influenced by factors such as the clarity of the atmosphere and the absence of competing light sources.
The choice of 30 miles as the average threshold highlights the sensitivity of the human eye in low-light conditions. It also emphasizes the importance of dark, clear nights for optimal visibility. This information is valuable in understanding the limitations and capabilities of human vision, especially in situations where minimal light is available.