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From: siegman@sierra.STANFORD.EDU (Anthony E. Siegman)
Newsgroups: sci.physics,sci.bio
Subject: Re: Magnetic Levitation of Organic Materials
Message-ID: <108@sierra.STANFORD.EDU>
Date: 16 Apr 91 04:38:59 GMT
References: <1489@gtx.com> <40065@fmsrl7.UUCP> <1689@sheol.UUCP>
Organization: Stanford University
Lines: 19

I>Well, I don't know how enormous you folks mean by "enormous".  But
>unless I'm much mistaken in my memory of reading the resulting images,
>MRI (the euphemism for what used to be called NMR imaging) involves
>subjecting a person to magnetic fields of between 1 and 2 trillion (as
>in 10^12) gauss.  The person I saw in the device didn't levitate.  Nor
>fry, nor heart-fail, nor nothing. 
>
>If I'm mistaken about the field strength involved in MRI, I'd appreciate
>being corrected.  As I said, I remember being somewhat amazed at a
>reading of 1.mumble terragauss on the statistics printed on the image
>output.

   The ac or radio-frequency field strengths (at frequencies something
like 30 to 60 MHz) would be very small, though I'm not sure about
terragauss -- that is really awfully small.

   What you more likely saw, however, was the _dc_ or _static_ field,
which is likely to be around 1 _Tesla_, which is the SI or mks unit
for magnetic field.  One Tesla = 10,000 gauss -- still _far_ below the