We present a study of the line-of-sight magnetic fields in five large-diameter Galactic H ii regions .
Using the Faraday rotation of background polarized radio sources , as well as dust-corrected H \alpha surface brightness as a probe of electron density , we estimated the strength and orientation of the magnetic field along 93 individual sight-lines through the H ii regions .
Each of the H ii regions displayed a coherent magnetic field .
The magnetic field strength ( line-of-sight component ) in the regions ranges from 2 to 6 \mu G , which is similar to the typical magnetic field strength in the diffuse interstellar medium .
We investigated the relationship between magnetic field strength and electron density in the 5 H ii regions .
The slope of magnetic field vs. density in the low-density regime ( 0.8 < n _ { e } < 30 cm ^ { -3 } ) is very slightly above zero .
We also calculated the ratio of thermal to magnetic pressure , \beta _ { th } , for each data point , which fell in the range 1.01 < \beta _ { th } < 25 .
Finally , we studied the orientation of the magnetic field in the solar neighborhood ( d < 1.1 kpc ) using our data from 5 H ii regions along with existing measurements of the line-of-sight magnetic field strength from polarized pulsars whose distances have been determined from their annual parallax .
We identify a net direction for the magnetic field in the solar neighborhood , but find no evidence for a preferred vertical direction of the magnetic field above or below the Galactic plane .