Formula works for one row does not for two

[ThomasL]

So, in essence, numpy does not like making the calculation of radians part of the equasion when there are more rows than 1.

No, the problem were all these float(df6['Latitude']) etc
to change the data type a column (series) in a dataframe you need to call the appropriate pandas methods to do so.
You can put the np.radians() back into the calculation and it will work also.