Introduction:
A dip circle is an instrument used to measure the angle of inclination (dip) of the Earth's magnetic field at a specific location. It consists of a magnetic needle mounted vertically on a horizontal axis. When the dip circle is aligned with the magnetic meridian, it provides information about the dip and declination angles.

Given information:
- Dip: 30 degrees
- Declination: 45 degrees

Determining the dip angle measured by the dip circle:
The dip circle is aligned with the geographic meridian, which means it is in the vertical plane passing through the North and South Poles. The dip angle measured by the dip circle will be the angle between the horizontal plane and the Earth's magnetic field.

Calculating the dip angle:
To determine the dip angle measured by the dip circle, we need to consider the given dip and declination angles.

1. The declination angle is the angle between the geographic meridian and the magnetic meridian. In this case, the declination angle is 45 degrees.

2. The dip angle is the angle between the horizontal plane and the Earth's magnetic field. In this case, the dip angle is 30 degrees.

3. Since the dip circle is aligned with the geographic meridian, the declination angle can be used to determine the orientation of the magnetic meridian with respect to the geographic meridian.

4. The dip angle measured by the dip circle can be calculated using the formula: dip angle = 90 degrees - declination angle + dip angle.

5. Substituting the given values: dip angle = 90 degrees - 45 degrees + 30 degrees = 75 degrees.

Explanation:
The dip angle measured by the dip circle in this scenario is 75 degrees. This means that the Earth's magnetic field is inclined at an angle of 75 degrees from the horizontal plane at the given location. The dip circle helps in understanding the orientation of the Earth's magnetic field, which is essential for various applications such as navigation, geophysics, and studying the Earth's magnetic field.