Gravity: We can use technology to measure its intensity as it accelerates matter, but this is not the same as rendering it "visible".
Photoconductivity serves as a tool to understand the internal processes in these materials, and it is also widely used to detect the presence of light and measure its intensity in light-sensitive devices.
Phototubes have been replaced by semiconductor-based photodiodes that can detect light, measure its intensity, control other devices as a function of illumination, and turn light into electrical energy.
In order to observe the magnetic field thoroughly, each satellite carries two magnetometers: a Vector Field Magnetometer (VFM) coupled with a star tracker camera, to measure the direction of the magnetic field in space, and an Absolute Scalar Magnetometer (ASM), to measure its intensity.
To further corroborate the activity-dependence of H2BE, we used GAP43-mCherry fluorescence as a reporter of H2be gene expression in H2be-KO mice and measured its intensity relative to that of tyrosine hydroxylase, a marker of neuronal activity in the glomerular layer of the olfactory bulb (Cho et al., 1996).
For those so inclined and the truly dedicated, you might also take along a portable radio frequency spectrum analyzer---the purpose of this is to detect lingering microwave energy and to measure its intensity at various points within the crop formation.
It then becomes necessary to stop the beam in order to measure its absolute intensity.
Each mutant clone was grown in a deep-well microplate containing 800 µL of the LB medium containing 20 g/L glucose for 20 h, of which 100 µL were transferred to a black microplate to measure its fluorescence intensity by adding LipidGreen1.
While measuring call intensity from wild animals is difficult, measuring its spectral correlates is not.
